worse than wack--it's derogatory fer sher
however--there is an alternate meaning to be used ONLY when it's REALLLLLY good.
bad: that guy is a smack-ass ho for coming to your party and actin' up like that.
good: we played a smack-ass game of poker last night and my boyfriend walked with the pot!
A person who constantly annoys people either for the fun of it or he/she is just completely stupid knowing that he/she will obviously get in trouble with a painful punishment (Hitting, yelling, scolding, grounding, etc).
"Could you get that little Smack-Ass off of my lawn?", "Keep that Smack-Ass away from me!", "You Smack-Asses are going to get it now!"