A saying from Tyneside (in the North East of England), used when expressing absolute confidence that something will not happen. It refers to Fenwicks' department store in Northumberland Street in Newcastle upon Tyne, which is famous for the quality of its window displays, especially at Christmas.

Similar in sentiment to I'll eat my hat.
If Sunderland finish above Newcastle in the league, I'll bare my arse in Fenwicks' window!
by Dommar41 March 4, 2012
Get the I'll bare my arse in Fenwicks' window mug.