This is where I first heard it as well. I remember that it stuck out as being novel in terms of crass humor, but according to the article the term predated it by several years at that point. Makes you wonder about what obscure new words are being used right now that you won't hear for another decade.

In my memory you had to craft it from two half-asses, but it looks like they were really called bum cheeks.

I remember first encountering the term on b3ta around the same time.