A guy goes to the supermarket and notices an attractive woman waving at him. She says hello. He's rather taken aback because although she looks familiar, he can't quite remember how he knows her. "Do i know you?" he asks.

She replies. "I think you're the father of one of my kids."

Aghast, his mind travels back to the only time he's ever been unfaithful to his wife. "Oh God, are you the stripper from that stag weekend that i had sex with on the pool table with all my mates watching while your colleague whipped me with wet celery?"

She looks at him in the eyes and calmly replies "No, I;m your sons teacher."