1. rude slang To be intensely annoyed or irritated. Everybody who lives on this side of town has a wild hair up their ass, thanks to the traffic delays from construction of the new inter-city tramline. After experiencing so much turbulence on her flight, Liz really had a wild hair up her ass when she arrived in town.

2. rude slang To be obsessed with someone or something, often when said obsession is strange or unexpected. I don't know why Mom has a wild hair up her ass about our trip. I've tried reassuring her that we'll be fine, but it doesn't seem to help.