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".
A great insult used by Donnie Darko. At the dinner table with his family directed twords his little sister
Donnie~ Your such a fuckass Elizabeth
Elizabeth~ Did you just call me a fuckass? You can go suck a fuck.
Donnie~ Oh please, tell me Elizabeth, How exactly does one suck a fuck?