The surprising likely origin of the word "bad" -- "effeminate man." From the Oxford English dictionary (OE = Old English, ME = Middle English):

Prof. Zupitza, with great probability, sees in bad-de (2 syll.) the ME. repr. of OE. bæddel ‘homo utriusque generis, hermaphrodita’ ... and the derivative bædling ‘effeminate fellow, womanish man ...’ applied contemptuously; assuming a later adjectival use, as in yrming, wrecca, and loss of final l as in mycel, muche, lytel, lyte, wencel, wench(e. This perfectly suits the ME. form and sense, and accounts satisfactorily for the want of early written examples. And it is free from the many historical and phonetic difficulties of the derivation proposed by Sarrazin [which ends up relating it to an OE. word meaning ‘forced, oppressed’] .... No other suggestion yet offered is of any importance; the Celtic words sometimes compared are out of the question.

The Random House and Webster's Revised Unabridged echo this; the Online Etymology Dictionary suggests that bæddel and bædling also meant "pederast."

Thanks to Language Log for the pointer. Naturally, I do not mean to imply that I agree with the thinking reflected in the etymology, much like I don't think that Slavs are naturally slaves. I just thought it interesting that such a simple, foundational-seeming term as "bad" appears to stem from attitudes about sex roles.