Boyfriends.: Prep said things like "hot choccy" and "choccy milk" a grand total of once or twice each, and it wasn't even focused on, but if you asked the comic's detractors (and even some of its fans), they'd have you believe it was his defining character trait and one of the reasons the comic is "bad".
A somewhat meta-example in Gunnerkrigg Court: In one page the readers didn't recognize Eglamore, so now whenever he appears, Tom will always point out to them that it's Eglamore.
He lampshaded this at one point by pointing out that "the girl next to Eglamore is Antimony Carver, the hero of this strip".
Homestuck: The fandom will probably never let John live down his "I'm not a homosexual" comment. Try to find one slash fic involving John where he doesn't say that or bring it up.
In Sidekick Girl, Illumina has a reputation for being a death magnet to her sidekicks (Part of the reason immortal Val was assigned to her). Only one, Val's immediate predecessor, actually died. Of her other long-term sidekicks, one quit on her in the middle of a fight and the other went insane from the stress of being an eternal twelve-year-old.
Monette in Something*Positive has since been adopted by the MacIntyres and become a successful actress. But, despite now being in a committed lesbian relationship, she'll be remembered as the most man-loving lesbian ever...who'd rather do animals than women.
During the chapter of Reynir's arrival, the idea of eating him if the crew ever ran out of food was brought up very briefly, and that same chapter ended with actual orders to the crew to keep Reynir alive. Several real life years later, comment quips about the crew's food reserves or cannibalism will inevitably find a way to involve Reynir.
Ever since Håkan Västerström cut Onni's ear in the real world right when he was getting a similar injury in spirit form, subsequent appearances of he and the siblings with whom he's The Dividual tend to make the readers a little more wary of them than strictly necessary. The three children have had two scenes ever since the incident, one playing in the background, one hovering over Onni during his Power-Strain Blackout coma.
