Bloke out walking his dog. The dog casts a look up at his owner, and the owner lets it off its leash. It runs up to a wall, puts its paws on it, flattens itself against the wall and takes a piss.

A man walking past observes this and remarks "Bloody hell, that's amazing!"

"Aye", replied the dog's owner. "He's been that way ever since the garden wall fell on him."