In "Night of the Living Laundromat" why couldn't the monster eat Jon's old plaid leisure suit? Simple: it had better taste than that!
In "The Carnival Curse", Garfield is turned into what's clearly a werewolf, but is never referred to as such and only called a "wolf creature". This is understandable when you realize "were" means "man", and Garfield becomes a cat-wolf.
In "The Perfect Match", Jon's favorite Marx Brother is Zeppo. Zeppo is considered the boring brother, playing the straight man to his brothers' antics, to the point where the "boring" member of a group act would be called "the Zeppo" (although, in real life, his brothers considered him to be the wittiest of them all, being able to imitate his brothers flawlessly). One of Jon's character traits in Garfield is that he's considered boring (at least by the standards of Garfield and Jon's dates) so it makes sense that Jon's favorite Marx Brother would be "the boring brother".
In "An Egg-Citing Story", a flashback is shown of Sheldon saving Booker and three other chicks from the weasel. This was the only time we ever see other chicks besides Booker and Sheldon living in the same farm, and we never see them again....What happened?!....Did the weasel (or the fox) successfully catch and eat the three chicks?!
Maybe they live with Roy's niece?
Played for laughs in-universe an episode of Orson's Farm titled "The Secrets Of The Animated Cartoon," in which Orson explains different cartoon tropes. The example given for the "extreme delayed reaction take" is Booker telling Bo that Earth is being invaded by aliens disguised as bottles of dishwashing liquid. No reaction. Months pass. Then, one snowy day the following winter, Bo suddenly stops dead and says, "Dishwashing liquid?! Aw no, man!" and flees in terror.
In "Fair Exchange", after Jon and Garfield have an argument, they both go to bed and dream about switching places. Most of the cartoon is Garfield learning how hard Jon has it and Jon (as Garfield) goofing off, but towards the end after Garfield wakes up, Jon is shown pleading not to be taken to the vet, promising to be a "good cat", at first it seems like nothing, then you realize Jon was talking about being taken to the vet to be put down. Yeowch! That's some dark humor for a cartoon aimed mostly at kids.
He might also be afraid of being neutered (which would still be pretty horrific, for a sapient human-cat).
A LITERAL version of this trope in one of Garfield's Tales Of Scary Stuff involves one of Jon's recipes coming to life. At the end, baking soda defeats the monster. A mostly silly episode, but what happened to the little girl at the end who didn't have baking soda? Most characters in Garfield's universe aren't as equipped to fight monsters as Garfield, Odie, and Jon are.
In one episode, Garfield uses a wishing well (that turns out to be a reality-warping alien) to eliminate Mondays from existence. The wish comes true, and Mondays are erased—but the implications, as hinted at in the episode, are truly terrifying. The U.S. education system grinds to a halt—since children start the school week on Mondays, their parents can't send them back to learn; any location that has trash pick-up on Monday can no longer have it, leading to massive piles of garbage spilling into the streets (which is a breeding ground for germs and disease); and whole types of businesses, such as gyms that offer "seven-day reducing plans" or movie theatres that change films on Mondays, have to close. Thankfully, Garfield undoes it—but not before the wishing well does even more damage to reality by eradicating "Thursdays, the state of Wisconsin, the entire month of August, chocolate candy, and everyone on the planet named Bob." It's all Played for Laughs, of course, and the wishing well's further changes only last a few minutes, but imagine what would happen if this really occurred...
On another note, when Garfield asks the alien's mother to undo her son's damages, he noticeably neglects to include undoing the disappearance of everyone on the planet named Bob.
Despite the episode's Tone Shift from gloomy and suspenseful to more comedic and surreal when he discovers the wishing well can talk and it turns out to be an alien, there's another fridge horror. What if the mother never showed up? Would the well have continued to eliminate things until it all disappeared?
In "Polar Pussycat", Garfield accidentally flies to the South Pole and is trapped with a man who tries to kill him and use his skin for gloves. During the man's last appearance, Garfield throws a bucket of water over him, and freezing his body over with ice and snow. We never see the man again. Did Garfield just kill someone?
In "The Wolf That Cried Boy", Roy plays a classic Crying Wolf joke with the "wolf alarm bell". The first two times, everyone immediately rushes to the bell, the third time (slightly subverting the usual Rule of Three in the moral) the gang ignore it for a few minutes then decide Roy must be telling the truth to keep carrying on like that. If Roy had been joking again, the fourth time they wouldn't have believed him 'at all' and the chickens would have been wolf food.
In "Hamelot" the farm gang were wearing swimsuits to take a shower. It would've been understandable if they were wearing swimsuits just for show and to go swimming. But wearing swimsuits to take a shower, when you need your clothes off anyway?
Maybe it hasn't occurred to them that they're all naked anyway.
Since when did Jon had a niece (from "Suburban Jungle")? He has one sibling and he's not married. Maybe Doc Boy adopted her?
He was also once going to mail a stuffed cat to his cousin. Perhaps it's one generation back - either his mom or dad had siblings and that's where these relatives are coming from.
Have any of you considered that Shannon's mom dumped Doc Boy?
Maybe Jon and Doc Boy have some sisters? While it's been established that Doc Boy is Jon's only brother, it's possible that they have sisters (who chose to leave the farm like Jon did) who have kids of their own.
It's also possible that it's an Honorary Uncle situation. In "Wedding Bell Blues," we meet his cousin Marion, so there are additional Arbuckles in the world. It's relatively common for complicated familial relationships (first cousin once removed, second cousin-in-law on the mother's side, etc.) to simply use the term "uncle" or "aunt" to describe "older male/female relative."
Roy's the only rooster on the farm and makes a point of driving off anyone who tries to take his job. Does that mean Booker and Sheldon are his children...?
How can the Buddy Bears talk with humans (meaning with their mouths), while Garfield and the other animals can't? Furthermore, how can they communicate with humans and animals (like Garfield in "Binky Gets Cancelled... AGAIN!")
Sometimes Garfield and other "talking" animals 'can' communicate with humans depending on the episode. There have been instances of Garfield saying something and Jon (or another human) responding to it, turning towards him when faced away, or show facial reactions. It's not uncommon for Garfield to make an aside joke at the audience and Jon to have a "very funny, Garfield" look on his face. A notable example is "Garfield's Garbage Can And Tin Pan Alley Revue", where Garfield is singing all night and doing "magic tricks" and Jon knows the song.
In "Sleepy Time", Lanolin introduces Orson to her niece, Shirley. Surely this must mean that Bo and Lanolin have a sibling we don't know about. That, or Bo has children and this is never addressed.
We know that Lanolin has a long string of relatives from the episode "Sleepytime Pig" (she gets them to form a conga line to help Orson sleep), so Shirley could be one of their kids.
and Jon's dates