From WordNet (r) 3.0 (2006) :
pain in the ass n 1: something or someone that causes trouble; a source of unhappiness; "washing dishes was a nuisance before we got a dish washer"; "a bit of a bother"; "he's not a friend, he's an infliction" [syn: annoyance, bother, botheration, pain, infliction, pain in the neck, pain in the ass]