WordNet sense 1 (the psychological state of being irritated or annoyed):

irritation, vexation, botheration

WordNet sense 2 (an unpleasant person who is annoying or exasperating):

aggravator

WordNet sense 3 (anger produced by some annoying irritation):

chafe

WordNet sense 4 (something or someone that causes trouble; a source of unhappiness):

bother, infliction, pain, pain in the ass, pain in the neck

WordNet sense 5 (the act of troubling or annoying someone):

annoying