We mentioned last week that the old expression buck naked sometimes appears nowadays, erroneously, as butt naked. A colleague shared our aversion to this misusage, and added that he was equally offended by those who write "He got a wild hair up his a.. ." The proper phrase is "wild hare up his a.. " our man said. I demurred. I was sure hair was correct. I still am — at least 90 percent — but I found that proof is harder to come by than I'd expected. Standard dictionaries don't list the phrase and some slang dictionaries don't either.
The on-line Urban Dictionary does list "get a wild hare," and says it means "to get a wild impulse," and it adds that "wild hair" is a "common misspelling of 'wild hare' (a 'hare' being a wild, rabbit-like animal)." So the UD, which is not always reliable, seems to agree with my colleague that the saying refers to one having a rabbit up his fundament. That would cause strange behavior, all right, but it's too much of a stretch for me. A hair rather than a hare is much more likely to be found on the terrain in question, and unruly hairs are sometimes capable of causing discomfort.
Another on-line dictionary says that "wild hair" is correct, and that to have one where the sun doesn't shine is "to be obsessed with some strange or offbeat idea." It doesn't explain why hair is correct, though.
The New Partridge Dictionary of Slang and Unconventional English comes down on the side of hair, and that's good enough for me. This is a two-volume update of an old and respected reference work. It says:
"wild hair — an impulsive notion. A shortened form of wild hair up your ass without the full connotation of annoyance.
'Something bothering you, Jimmy? You got a wild hair?' Robert Campbell, Nibbled to Death By Ducks, p. 68, 1989."
"wild hair up your ass; wild hair up your butt — the notional cause of irrational, obsessive behavior.
'I was over there behind your friend with the wild hair up his ass.' — Thomas Harris, Red Dragon, p. 184-185, 1981.
'Jeez, don't get a wild hair up your butt.' — Cherie Bennett, See No Evil, p. 147, 2002."