A person that has a face that looks like a butt and is very violent. Their face (which is a butt crack) holds a knife that they bring out to kill. He also walks around not knowing where he is going due to his butthole being his eye. After the kill, he goes to the bathroom to drop a fat nuke.
Watch out for the Butt FaceKiller is walking around so keep your distance or he will kill and drop a fat nuke.
This isn't really a harsh name to call someone at all. More times than not it is used by close friends especially male/female friends or even siblings. There is a major difference in calling a person an "Ass head" as compared to "Butt Face"
"Hey what's up buttface?" "Are you going to make the birthday party on Saturday?"