With a battleship mouth and a rowboat ass
He calls folks liars with his lack of class
Hidden in the bushes he barks out lies
While as a kid he pulled wings off flies
He thinks hes clever but hes just a ________

I'm stumped. Cant say horses ass because of the first line, pompous, long-winded jerk doesnt rhyme, but thanks to your suggestion, Ill use dumbass. Dumbass is kinda juvenile, but it was your suggestion. We make a great team. You give me so much to work with.