"First Time [Insert Character Name Here]"
Just is BM imo; when the skill level seems good but someone claims to be a first time player of a given champion? That is the most insulting thing I can think of aside from wishing cancer on someone in game.
I don't claim to be perfect nor do I not have my toxic moments, but this is one of my biggest pet peeves.
TL;DR: Don't pee on my leg and tell me its raining.