(slang, pejorative) An obnoxious or contemptible person; a jerk.
2000, Martin DiPietro, "The Pull" in Nest: 28 Tales of Pulp Fictionhttp://books.google.com/books?id=8-Ktus3DJ3EC, ISBN 0595140653, page 72:"Look," said Mayer, suddenly nervous, "there's no sense in acting like complete ass monkeys over this. I'm sure we can reach a mutually beneficial settlement."
2002, Brian Rockstroh, Far From Gracehttp://books.google.com/books?id=YMG2M2bMBLkC, ISBN 0595222307, page 10:“You little assmonkey!†The kid danced away to the front of the car.
2004, Stacey Cochran, The Bandhttp://books.google.com/books?id=04WwRTaaoUAC, ISBN 1411607589, page 188:"God, love," I said, "Annnnnd ... trampolines!" ¶ "You are such an assmonkey."