Ballbag

n.

Heard in Dublin, Galway, Sligo and Limerick

A vulgar term for a man's testicles, often used to express a flat refusal.

In use

Will I lend you a tenner? Ask me ballbag la!

Posh English

Would I care to lend you ten pounds? You might as well inquire of my testicles, old chap!

Same phrase, other counties