A close relative of an asshat, an assmonkey is best defined as 'any disagreeable idiot who has successfully combined being an asshole with the brainpower of a monkey fed LSD'.
Eytemology is unknown, but there are perhaps links to Wayne's World, and the line "Pshyeah, and monkeys might fly out my butt."
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"