I'll bare my arse in Fenwicks' window
A wild threat from the North East that means you’re so sure something won’t happen, you’d rather show off your backside in a fancy shop window than be proved wrong.
He said he’d bare his arse in Fenwicks’ window if the traffic didn’t clear before 8 a. m.
She told her boss she’d bare her arse in Fenwicks’ window if the project wasn’t done on time.
He bet his lunch money he’d bare his arse in Fenwicks’ window if the team didn’t win the match.