Numpty

n.

Heard in Dublin, Cork and Wexford

A foolish, thick-witted person prone to bouts of supreme idiocy.

In use

Jaysus, don't mind a word he says, sure he's a bleedin' numpty!

Posh English

Good heavens, pay no attention to his utterances, as the fellow is a confounded nincompoop!

Same phrase, other counties