I was in the pub with my mate last night when he said to me, "Look, mate, I've been having an affair and my wife's getting suspicious. If she asks, I was with you last night."
I nodded. "No problem."
A minute later, his wife came into the pub and said straight at me. "Dave wasn't home last night - I think he was sh*gging some sl*g!"
"No, he wasn't," I replied immediately, winking at him.