the term ass jack-o-lantern is a somewhat more clever and (perhaps?) less childish way to call someone a butthead. it also implies that the person has a nasty face and is an enormous creeper (both of which are qualities possessed by a halloween jack-o-lantern)
the ass jack-o-lantern dated the girl that was way too good for him and wore a stupid hawaiian shirt.
Used to describe someone who is extremely good at Anal sex be it receiving or giving or both, sometimes better than oral sex or vaginal sex
girl 1 : "you were right he left my ass sore and my pussy sopping, never thought anal could feel that good"
girl 2 : "Told you he was a assmancer, whenever we do it he leaves me soaking the bed"
"dat was S-class ass, damn she a true assmancer, had me busting under minute"