Gombeen

n.

Heard in Cavan, Kilkenny, Cork, Waterford, Limerick and Tipperary

A foolish, blundering, or simple-minded person.

In use

Shut yer mouth ya gombeen, she'll hear every word ya're saying!

Posh English

Shut your trap, you absolute simpleton, she will overhear you.

Same phrase, other counties