I have a few:

open mouth chewers - this makes me almost go postal, it's SO GROSS!!

when people wear flip flops and drag their feet on the ground - pick up your heels!!

when people don't use their turning signals - it's as if they're the only ones on the road or they expect you to read their minds. And similar to this one, I hate it when police patrol cars don't bother signalling - how can they enforce regulations if they themselves won't??

dog owners who don't pick up after their dogs - gives responsible dog owners a bad rep.