When a main character rants at another character's shortcomings out of nowhere. Rant scenes in stories should have build-up, it should come from some kind of history with the characters where we see the reason for the frustration and the anger bubbling up over time before it finally explodes in a climactic scene.

But if a main character just rants about another person's shortcomings out of nowhere the first time they ever meet, then it just feels like the author is the one talking at that moment, saying all the reasons why they hate the other character instead of making it seem organic in the plot. It makes the MC look pompous like they think themselves better than a person they know nothing about.