Biggest fanfic pet peeve?
It's probably a toss up between the wall of text (impossible to read so I don't even bother trying) and... a story that tells you everything straight up. Maybe that second one isn't really a peeve, but I'd much rather read a story with some subtlety, that lets the reader try to figure things out through the character's actions rather than just being told what happens. I also like stories that end with a bit of a grey area, where the reader can sort of fill in their own ending. Kinda like the way The OC ended with Ryan and Taylor. Did they stay together? They gave each other that look, but we don't know, and the viewer can draw their own logical conclusion.
I don't like being told every little thing, I guess. I don't want to read a fanfic that tells me every single thing about the character's lives. Tell me about a story that happened in their life - not their life story, you know?