I disagree with using "dumbass" as a contraction. GP poster had it correct, in that he was describing the previous poster's ass as being dumb. On the other hand, "dumbass" is a pejorative describing a person, literally a "stupid donkey". Now, I'm guessing the former version is a derivation of the original "dumbass", which was probably "dumb ass" at some point as well. Some examples, with everyone's favorite contraction:
"You're a dumbass."
"Your ass is dumb....your dumb ass".
See the difference? It wouldn't work well to say "Your dumbass" as that would imply that he either literally owned an unintelligent donkey, or that he had a dumbass working for him:
"Yo, your dumbass you sent down here to fix the pipes made things worse!"
And for mods, this is all very relevant to the article topic - after all, there's nothing more important than being able to correctly insult people on xbox live. Let's keep it horribly racist, sexist, demeaning to all cultures, and grammatically correct out there fellas!