Adjective. Used to describe someone or something that is attractive. Does not have to refer to the back end of the object, simply to the way they appear. Can also be used with suitable prosodic features to be sarcastic.
1. A humorous exclamation uttered whilst playing a game, and while playing, the game characters unintentionally do something suggestive, for example, when playing Star Wars Battlefront, and you use the crawl feature and make the character back up, causing them to crawl backwards with their ass in the air. At that point, it is prudent to say "Sexy Ass!" to provide comical relief.
*Playing Battlefront II as Aayla Secura:
me: Sexy Ass!
crazedgamer24 (a.k.a. Fuck Bag): lol!
A Sexy Ass is a semi-rare phenomena occurring on a woman's backside. A Sexy Ass is generally round and malleable, with a consistency similar to dough, but reshapes itself to it's original form when no longer touched.