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Jerkass Ball or Conflict Ball if they act hostile out of character. Not sure about random strangers. Perhaps Chandler's Law.
Edited by eroockChandler's Law looks good to me.
If the character comes out of nowhere and gets no established motivation before or after the conflict scene, then the character is being used as a plot device. But I can't offer anything more specific.
Edited by FerrousFaucetChandler's Law is a bit too specific but I guess it's the best we have. Both scenes I was thinking of involved characters being randomly dickish in a bar (randomly insulting the protagonists as their introduction), mostly for the point of starting a fight in said bar. The characters don't come back after this so we have no idea what their issue was aside from arbitrarily not liking the main characters. But this is probably too specific to really have a trope for. (In one of them it at least establishes that neither of the protagonists are respected, making them outcasts through the display of spontaneous bullying; in the other, it really is just for the sake of a fight scene)
(I mean, there's stuff like Jerkass, obviously, was just wondering if we had something more specific for a character we know nothing about showing up to start conflict before disappearing)
Edited by WarJay77 Working on: Author Appeal | Sandbox | Troper WallI suppose...
I do think that the "establishes them as outcasts" version could fit nicely into a trope concept I've been toying with for a bit now. Otherwise this is probably just too niche, and covered by much broader concepts.
Working on: Author Appeal | Sandbox | Troper Wall

When a character picks a fight or acts like a dick for pretty much no reason other than that it's what the scene requires. I wouldn't file this under Kick the Dog because these are usually characters we don't see again, their entire role is to be an asshole for no discernable reason and create drama for a scene. (It's because we never see them again that we can't even label it as something like bullying or a grudge, because it comes out of nowhere and the character gets no established motivation).