I'll start with the most obvious:
*clears throat*
RARE!!!
Why must every seller punctuate a listing with "RARE!!!"? I mean, underneath it all, I guess I understand the logic of it -- sort of -- but it really bugs me on a basic human level. The real rarities take a hit every time someone claims that Tetris or John Elway's Quarterback is a "rare" game.
Anyway.
Who else has a term they're tired of hearing on eBay?