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 monkeyfedLSD'.
Eytemology is unknown, but there are perhaps links to Wayne's World, and the line "Pshyeah, and monkeys might fly out my butt."
"God, could Nicholas be any more of an assmonkey? RTFM, n00b."