A big, self-centered motherfucker, who also happens to be an asshole. When the two words are combined, (due to some complex limits) the included noun "hole" works to cancel out the word "mother" and for some unknown reason, "fucker" becomes "fuck". the result is the word "fuckass" (fuhk-as).
Also, this word may be useful on a tertiary level, in the event that the person of reference is homosexual, or in some way involved in bum-sex, in the sense that it could describe the action of "fucking the/an ass".
That Adam guy was a fuckass huh?
Yeah, pretty much