Here's a one from Snatch.
Turkish: Fuck me, hold tight. What's that?
Tommy: It's me belt, Turkish.
Turkish: No, Tommy. There's a gun in your trousers. What's a gun doing in your trousers?
Tommy: It's for protection.
Turkish: Protection from what? "Zee Germans"? What's to stop it blowing your bollocks off every time you sit down?