Chuck, played by Londoner Ed Westwick, gets his haircuts at Piccadilly.
Blair compares Chuck to House. Leighton Meester guest-starred on House, playing a teenager with a huge crush on the title character. Coincidentally, Chuck and House are both dark, twisted Jerk with a Heart of Gold type characters, and Ed Westwick and Hugh Laurie are both Englishmen while their characters are American. What makes it funnier is the scene where Chuck is talking to Blair about her British boyfriend and says: "You can't tell me Bertie Wooster is satisfying your needs."
Blair mentions herself and Chuck role-playing "Wuthering Heights". Ed Westwick had been cast to play Heathcliff in a new remake but was dropped not long before the episode where Blair makes the mentioning aired.
As a side effect of the show's Idiosyncratic Episode Naming, season four's "The Townie" references The Town in which Blake Lively has a role. The same season also saw "Panic Roommate" mash up Panic Room and The Roommate (Leighton Meester plays the title role in the latter), and "Easy J" riff on Easy A (in which Penn Badgley appears). The first season also has an episode called "Blair Waldorf Must Pie!" (from John Tucker Must Die, which also has Penn Badgleynote and Brittany Snow, who played as the young Lily Van der Woodsen in the Valley Girls episode.) and the Series Finale is called "New York, I Love You XOXO" (after New York, I Love You, with Blake Livelynote and Rachel Bilson, who has an uncredited cameo in the episode).
In Season 1 when Jenny is trying on dresses at Blair's house, Blair tells her a dress is too Hannah Montana. Taylor Momsen was one of many actresses considered for the role.
During the build-up to and actual Blair's wedding, Wallace Shawn makes at least two Princess Bride references by name.
In Season 6, Chuck tells Nate that maybe he needs to find himself a Hot Tub Time Machine. Former guest star Sebastian Stan (Carter Baizen) starred in this movie.
In the final season's "It's Really Complicated," when Serena tells Blair that her ex Steven (played by Barry Watson) tried to get back with her, Blair (who'd rather it was him than Dan again) replies "Ooh, you must be in 7th Heaven!"
Approval of God: Cecily von Ziegesar, author of the original books, liked all the representations of her characters. The exception is Vanessa - who is a bald Goth in the books and gets Adaptational Attractiveness to be played by the very pretty Jessica Szohr in the TV show.
Breakup Breakout: Out of all the main characters, Blake Lively and Penn Badgley were the only cast members to find mainstream success after the series ended. Though Taylor Momsen did have a successful music career after retiring from acting.
California Doubling: Defied. The network wanted the show to be filmed in Los Angeles, on sound stages recreating locations like Central Park. Stephanie Savage however fought for it to be filmed on-location in New York, feeling the city itself was a character.
Blake Lively later called it "emotionally compromising" to play Serena, and hated filming all the sex scenes. (It's telling that unlike Leighton Meester, Lively never put her work up for Emmy consideration.)
Chace Crawford (Nate) didn't enjoy his time on the show either and was glad when it finally ended.
Penn Badgley confessed in interviews that he grew to hate his character, finding Dan to be a raging hypocrite. He also didn't take too kindly to The Reveal that Dan was actually Gossip Girl all along, finding it as much of an Ass Pull as fans did.
Ed Westwick did also not approve of some of Chuck's more deprived actions. His mother, a psychiatrist, would call him up after certain episodes and tell him she's worried about Chuck.
While Leighton Meester has said that the show was "very special" to her, she feels that it wasn't a particularly healthy environment; due to the sixteen-hour filming days and the intense media scrutiny the young actors were under.
Creator's Apathy: Taylor Momsen admitted to being burnt out with acting in general by the time of the fourth season; having been pushed into modelling and acting at the age of two, she was burnt out by the time she was sixteen. She would bring a guitar to set every day, not wanting to fully be there. She has however spoke gratefully of the producers for releasing her from her contract, allowing her to go on tour with The Pretty Reckless.
All the main "teen" cast, with the exception of Jenny apply into this trope. Particularly notorious is Nicole Fiscella (Isabel Coates, one of the mean girls), who was born in 1979.
This ended up affecting the plot of the show, as there was supposed to be a romance arc for Jenny and Nate, but Chace Crawford (22 at the time of filming season two) did not feel comfortable making out with Taylor Momsen, at the time 15.
An example for season 6 is Sage who is 17 played by Sofia Black-D'Elia who was born in 1991, two calendar years older than Momsen.
Defied to an extent by Kristen Bell. She was interested in the project after Veronica Mars wrapped, but realized she was too old at twenty-six to convincingly play one of the teens. So as a compromise, she provided the voice of the eponymous Gossip Girl.
Enforced Method Acting: Billy Baldwin refused to meet Blake Lively before their first scene together because he wanted the experience of seeing your father/daughter again after 14 years to be as real for both of them as possible. He also stated that he pretended Blake was his real-life daughter.
Fake Brit: Lord Marcus, played by American Patrick Heusinger. Making it an American playing a Brit who fakes being American. Add to that the scene where Chuck (played by a Brit, as noted above) imitates Marcus' accent to pull a Bed Trick on Blair. A Brit playing an American faking a British accent as done by an American.
Hostility on the Set: There was reportedly tension on the set between Leighton Meester and Taylor Momsen; supposedly stemming from both pursuing music around the same time. Leighton (who was singing solo) had her music featured on the show, while The Pretty Reckless (Taylor's band) wasn't. The CW even released a statement bluntly saying that the latter would be featured when it was "ready".
Leighton Meester appears to have fallen headlong into it. Despite well-received performances in several films, most of her mainstream work flopped, and audiences weren't able to see her as anyone besides Blair Waldorf.
Seems to have worked out better for Blake Lively, who did her hardest to avoid this - including taking drastically against-type roles in The Town, The Age of Adaline and in A Simple Favor. Along with gaining critical acclaim for some of those roles, she's also become well-known for her relationship with Ryan Reynolds. While the public still probably remembers her as Serena, that is unlikely to stop her from getting other roles, and the audience likely recognizes her from other works as well.
One-Take Wonder: Kristen Bell remarked in a career retrospective that the Gossip Girl narration was the only time in her career that she was "never given a note".
The Other Darrin: Florencia Lozano plays Eleanor Waldorf in the pilot. Margaret Colin replaces her for the remainder of the show.
Matthew Settle was at the time best known for playing creepy or ambiguously psychotic characters, most famously Captain Ronald Speirs in Band of Brothers.
Chuck's trademark scarf sold out within days of the pilot episode airing.
A more general example is that there was a Gossip Girl inspired clothing line produced, of cheaper versions of the designer labels the characters wore.
Stillborn Franchise: 2008 saw the release of OMFGG – Original Music Featured on Gossip Girl No. 1. There would not be a No. 2 (the CD didn't even include the show's opening/closing music for some reason).
This ad-libbed dialogue in the last scene from season two:
Blair: (after Chuck told her he loves her) But, can you say it twice? No I'm serious, say it twice.
Chuck: I love you. I love you. That's three. Here's four - I love you.
The first season received numerous complaints from the Parents' Television Council for being "mind-blowingly inappropriate" and "every parent's nightmare". The show ended up using those as taglines.
The concept was first pitched as a feature film with Lindsay Lohan as Blair and Justin Chatwin as Nate. Plans fell through, and the decision was made to pitch it as a TV series instead.
Nate and Jenny's relationship wasn't supposed to end so suddenly, but Chace Crawford was uncomfortable regularly making out with a teenager and supposedly asked for it to be ended.
A spin-off set in The '80s and revolving around a younger Lily was planned. The pilot aired in Season 2 and the show was picked up, but canceled before airing.
Connor Paolo turned down repeated offers to upgrade Eric to regular cast member for "personal reasons". When he became a regular on the ABC series Revenge, he left the series completely.
Word of God: Josh Schwartz and Stephanie Savage have cruelly crushed hopes for Vanessa/Rufus, saying that fans who want them are barking up the wrong tree.
Writing by the Seat of Your Pants: The true identity of Gossip Girl was something the writers very obviously didn't know as the show went on, and so the series seemed to be written as if it was never going to be revealed. When it came to do so, they instead changed who it was after allegedly the identity was leaked online. Tellingly, most of the actors mentioned having no idea who Gossip Girl truly was until the finale.
before Blake Lively was cast.