These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Better on DVD: A rare printed comic example: at least one strip made a lot more sense in the book collections, as the next day's strip completed the gag.
Broken Base: There are many fans who think the comic's still pretty funny, and many fans who believe the strip ran out of jokes in the mid-90's and jumped the shark when Jon and Liz got hooked up, and still others who think said hook up helped revitalize the strip.
"As a joke, I have tied Jon's shoelaces together. And as a bonus joke, I have attached this rope to an airliner about to leave for Italy."
A spider trips and his contact falls out. Garfield squishes the spider with a newspaper... then after a Beat Panel, crushes the contact lens too.
Deader Than Disco: In The Eighties, the strip was really hot stuff. Besides its insanely high marketing, it actually had a few strips that were considered controversial before essentially becoming one of those "love to hate it" strips.
Jon almost constantly calls Garfield fat in some of the most degrading ways possible, and it's played for laughs. Now realize that Garfield is fully sentient and can communicate in-universe.
In another strip, Jon intentionally doesn't buy Garfield kitty treats "because life's not fair." Even though it only happened in that one strip, it can still come across as a harsh thing to do to one's pet. Jim Davis must have been in a bad mood when he wrote that one.
Though Garfield has undoubtedly earned all the verbal shots, the punchline of one strip was Jon throwing Garfield through a glass window for making fun of his terrible suit. He probably got off easy thanks to Cartoon Physics, but still...
As pointed out in some of the comments, Garfield's reaction to Jon's statement here was rather mean.
"Funny Aneurysm" Moment: That time when Garfield said "We cats nap anywhere, anytime. Everyone should be so lucky. With the possible exception of airline pilots.". In 2011, there were many cases of airline traffic controllers sleeping on the job and tragic accidents ensuing as a result.
One strip◊ has Jon saying "We all have to live together. We all have to be considerate of our neighbors." The final panel shows Garfield in woman clothing as Jon yells "SO RETURN THOSE TO MRS. FEENY!". This was written in advance like all comic strips, and what day did it get printed on? September 11, 2001.
Nausea Fuel: After commenting on his coffee being too weak, he dumps it into Jon's shoes. Jon then wrings it out of his socks and into Odie's dish. Odie begins lapping it up, finds that it tastes horrible, and subsequently dumps it back into the coffeepot. Garfield takes a drink and says, "Much better." Watch it adapted into Garfield and Friends in its entirety.
Viewer Gender Confusion: Nermal, made only more confusing by his female voice actor on Garfield and Friends. The Spanish dub referred to Nermal as gatita (female kitten) before finally correcting it in the later seasons.
We're Still Relevant, Dammit: In the May 7, 2006 strip,◊ Garfield listens to the sound of bacon frying on an iPod. This manages to be both a parody of this trope and a straight example at once; it could've worked in the 1980s with a Walkman, or in the 1990s with a portable CD player.
What an Idiot: So many examples that it should have its own page.
September 3, 1988: A mouse is loose and Jon wants Garfield to kill it by telling him to "act like a cat." We know what Jon means when he says this, but Garfield, thinking conversely, promptly falls asleep.
August 23, 1995: Garfield and Odie have a "Do-Nothing Contest," and Odie wins. Upon hearing his victory, Odie gets up and cheers. Now Garfield wins.
The Scrappy: In-universe, Garfield sees Nermal this way.