Originally posted by: Amused
There's a lot of arguing going on amongst linguistics experts about the origin of this word (if that's what you call it). The first thing to know is that nobody really knows how to spell it since P.U. isn't an abbreviation of anything. Here are the two explanations I heard the most (and believe me, asking a bunch of people what the origin of P.U. was a hell of a way to start off a conversation).
1) It's a shortened term for puteo, which is Latin for "to stink, be redolent, or smell bad." I actually called a professor of Latin at the University of Florida to verify this one.
2) It's actually spelled "piu," but is often pronounced as "pee-yew". It's root is the Indo-European word "pu," meaning to rot or decay. A lot of other languages use this root word and have the same general meaning.