Batman Beyond: Terry and Melanie's relationship in the cartoon was already a borderline case because of the brief timespan over which it occurred, but it fully falls into this in the 2016 run of the comic. Almost a decade after their two short relationships that totalled less than a week, Melanie is still completely in love with Terry and making all of her decisions based on what she thinks will impress him. When they see each other for the first time in years without masks, they start kissing, while Terry is still with his longtime girlfriend. A few issues later and they're dating and talking as if they've known each other for years, and Terry still hasn't had an on-screen breakup with his girlfriend.
Hellblazer: Epiphany Greaves and John Constantine's romance sees them quickly thrown together with little to no actual development. Furthermore, it results in John acting extremely out of character on multiple occasions. To add insult to injury, John's exes show up for their wedding... and they're all portrayed as being jealous, with any other characterization being thrown under the bus in a failed attempt to make the pairing (and Epiphany) look better.
Subverted in the Infinite Crisis storyline "One Year Later". It had Diana suddenly involved in a relationship with Nemesis (Tom Tresser), a new co-worker and long-time minor DC character. Many fans felt this new hookup was rushed at best, especially since Tom was considerably more boorish than in previous appearances. Eventually, in Wonder Woman #32, it's revealed that Diana never loved Tom at all; she kinda liked him but was mostly just exploiting his feelings towards her to get him to father her daughters and replenish the Amazon population. So, instead of her loving a jerk, she's a borderline sexual predator taking advantage of his feelings.
Downplayed in a two-issue story arc in Aquaman following Aqualad visiting his mother's homeland of Xebel. The very first person he meets is a gay Xebellian soldier called Ha'Wea and the two are instantly attracted to each other and immediately begin flirting, despite the fact that Jackson is on an extremely time-sensitive mission and can't afford to be distracted, and Ha'Wea should probably be arresting him as an unidentified intruder. To be fair, they are shown having a long conversation demonstrating that they have as much in common as a kid from New Mexico and an undersea peasant can have, and at the end neither of them declares the other to be his one true love and drops his entire life to be with him, it's more of a "call me" situation.
Supergirl (1982): Philip Decker was deemed by Supergirl fans as a lame Creator's Pet kind of Love Interest early on. In his first appearance, Linda right away gushes over how he is the super-famous musician Philiph Decker and she is such a big fan. Four pages later, Phil casually meets Linda and asks her out right away...before reminding himself about another prior engagement and taking a rain check. From that point onwards, the story (which never bothers to explain why Phil likes Linda to start with, especially since dating with her is clearly inconveniencing him) and the secondary characters act like they are having a passionate romance, even though their whole relationship consists of Phil cancelling dates using transparent lies, Linda demanding an explanation, and breaking up with him when Phil refuses to give one. It does not help that Dick Malverne -another Supergirl's love interest, except that he actually had a proper build-up and was well-liked by long-time readers- returned to the series after a long absence, and Kupperberg revealed he brought him back only so that Supergirl went on an unwarranted rant against him.
Supergirl (Rebirth): As soon as Benjamin Rubel appeared, he was regarded by long-time Supergirl fans as the newest addition to the long list of SG's lame love interests who would be gone and forgotten when his creator left. During Orlando's run, those fans found him boring, sometimes obnoxious, and often a load for Supergirl. His relationship with Kara was hardly built on before becoming official, and it was over two issues later when, as foretold, Orlando left and Ben vanished and became forgotten.
Superman: During the New 52 era, editors were that adamant on pairing Wonder Woman with Superman, that they did not dig much deeper for chemistry than the obvious "they're both famous Flying Brick heroes with primary-color outfits." They had exactly one short and mundane exchange before dating without seduction period, while Wonder Woman dumped her ordinary, yet irreproachable usual boyfriend Steve Trevor with no explanation. Then the path to Superman and Diana’s rupture was full of petty arguments, proving they had not much in common, in fact, something not helped by Diana being heavily written as a violent warrior at the time. To make things even worse for Diana, Superman was as usual actually attracted to Lois Lane but put it on hold as she was dating someone else when they met that time. (Not that their shared book wasn't seemingly aware of it; a few issues had Diana become a writer.) In the subsequent continuity overhaul, Rebirth, the situation came back to normal, as the pre-Flashpoint Superman took over and was married to Lois Lane. Superman Reborn went as far as to remove the entire Clark/Diana relationship from continuity.
Kendra Saunders with Carter Hall. It was seemingly meant to be a deconstruction of Hawkman and Hawkgirl's eternal love, as Kendra was a reincarnation of Hawkgirl who not only didn't remember her previous lives but also didn't have feelings for Carter, preferring a Screw Destiny view of her fate. Meanwhile, he assumed they'd be together because that's how it had always been. Kendra was in relationships with other characters, while Carter was very publicly projecting his expectations and feelings for Shiera onto Kendra. Then she suddenly started showing some attraction to Carter. Finally, in Blackest Night Carter casually insults and rebuffs his best friend, leading Kendra to decide how hard it is not to love him, fullfilling the prophecy that they declare their love just before they die in each incarnation, as they die in that very same issue, Kendra's last words being a proclamation of love for Carter.
Katar and Shayera Post-Crisis. In Hawkworld, he's a Defector from Decadence who is frustrated with his society's class system and his people's treatment of other races. So obviously he falls for... Shayera, who publicly torments a servant right in front of him and callously murders what she considers lesser life. There is actually zero reason given for his attraction to her, as it's made clear that her behaviour disgusts him. Unless he just thinks she's hot, but after her death, he plays it up as some significant relationship.
The Official Couple of the DC Rebirth series was Carter and Shayera. Since they had spent most of their lives on different planets, they had had no personal interactions before she showed up to stop him (briefly possessed by an evil past life) from killing a bunch of people. From that moment on, they and everyone around them simply took it for granted that they were together because they are Hawkman and Hawkwoman. They both speak as if they have a long history together, which in a sense they do, but it doesn't change the fact that as individuals they had never met up until that point. It actually seems fairly plausible from Carter's side of the relationship, since the series had gone to great pains to show how important Hawkwoman has been to him over their lives together and he is characterised as very world-weary and weighed down by his history and memories, so it makes sense that he would be eager for companionship from the only other person who would understand. However, Shayera was previously in a relationship with the deceased Katar Hol (who is explicitly noted to be one of Carter's previous reincarnations) and when she appeared in Justice League only a few months before joining the series, she was still mourning Katar and had definitely not moved on, as she had created a realistic simulation of him to quell her loneliness, so her immediately jumping into a relationship with Carter is problematic at best.
Donna Troy and Terry Long. You'll hardly find anyone who likes the pairing. They had non-existent chemistry, and it doesn't help that Terry was a sleazy Wolfman look-alike. Or he was ten years older than her. Or he was her college professor. Or Terry's ex-wife predicted he'd divorce Donna because he feels emasculated by her and gets bored easily (which is exactly what eventually happened). Or he took their son away from Donna because she was a "bad" influence...
Tim Drake (Robin III) and Cassie Sandsmark (Wonder Girl II). Given the fact that they had a very platonic interaction before the hookup, that Wonder Girl was the girlfriend of Robin's dead best friend Superboy, and the reason they kissed in the first place was due to mutual mourning of said person... yeah, it was definitely a trainwreck. Fans of both Wonder Girl and Robin sighed a collective breath of relief when the pairing didn't go anywhere and was allowed to end.
Titans (Rebirth) has quite a few in one issue no less. One issue focuses almost entirely on the romantic troubles of the team, like a love triangle between Wally West, Donna Troy, and Roy Harper. Wally has shown zero feelings for Donna, but they end up making out because Linda Park "breaks up" with him (they weren't a proper couple anymore) and both understand what it's like to have messed up memories. Rushed, to say the least, but at least logical. The worse offender is Lilith and Garth, who get together because... no reason stated. And they've barely interacted before this issue. But because Lilith is a psychic, she says she's known that Garth has been hiding his feelings for her.
In general, it has quite a few because of its very nature. Because it's a return to DC's roots and a spiritual return to the pre-Flashpoint universe, it has a lot of characters that were Fan-Preferred Couple but weren't couples anymore (as a result of Flashpoint) getting back together. The problem is that it rushes them quite a bit because it assumes a level of familiarity with the reader.
An example would be Green Arrow and Black Canary suddenly pining for each other after one meeting (where they didn't even speak) in DC Universe: Rebirth #1. Their relationship was expanded upon in the Green Arrow (Rebirth) series where it made more sense, as the two actually got to know each other, at least.
From that same issue, Wally West and Linda Park. It works a little better since Wally explicitly remembers the timeline pre-Flashpoint (though Linda doesn't), but it's still weird for new readers who don't know about the two. He does explain why they fell in love, but it's a case of him telling not showing, as you just can't condense over a hundred issues into a single scene. This version of their relationship was also prevalent in Titans (Rebirth), where it ended with the two never becoming a couple like Wally wanted. To say fans are not amused when it comes to the handling of the Flash couple is an understatement.
Tim Drake and Stephanie Brown in Detective Comics (Rebirth) suffered from the same problem as the above. Many don't like that Tim and Steph were depicted in a relationship together with no prior buildup. James Tynion assumes a lot of familiarity and fondness for the characters and their relationships from the pre-Flashpoint era, and as such lots of the relationships, romantic or not, come across as sudden.
Speaking of poor Tim, there's the recent development of him and Bernard Dowd. It's not that the pairing is bad, as making Tim bisexual gives him a bit of uniqueness the other Robins don't have. It's that the writer for his adventures, Meghan Fitzmartin, is beating readers over the head with how the two are meant to be and disparaging the Tim/Stephanie shippers and Stephanie herself in the process.
JLA: Act of God: Superman and Wonder Woman, considering that Lois is pretty heavily derailed in order to break up with Clark. That said, both Wonder Woman and Superman undergo some fairly odd changes in behavior and worldview to come together in the way they did.
Brightest Day: Boston and Dawn's romance comes off more as pandering to male wish fulfillment than a meaningful relationship. It's really just there to give Boston an ideal supportive female for whom he can selflessly sacrifice himself in the end and Dawn shows no real romantic interest in Boston. She is friendly, but nothing would imply she's attracted to him. It's no wonder that it quickly died not soon after, despite being one of the few things to carry over into the New 52 reboot.
