gag

A joke, especially one that defies any logic or already established rules in the media it takes place in. These can standalone comedic moments (e.g. someone unexplainably using lazer vision, only for them to never use it again), single appearance characters (e.g. Arale Norimaki annihilating Vegeta out of nowhere despite his godly training in Dragon Ball Super), or be permanently applied to main characters (e.g. Saitama being completely overpowered compared to everyone else for seemingly no reason in One Punch Man). Also, see "gag character."

Vegeta: "I am never fighting someone from an 80's gag manga again!"