A guy is at the supermarket when he spots a good looking young woman looking directly at him. She waves and walks up to him. "Do I know you?" he asks. She replies "Actually, I think you're the father of one of my children". Gobsmacked, he tries to think of when this could have happened, and finally it dawns on him. "Oh my god, you're the stripper from my stag night, aren't you? I've never been unfaithful to my wife any other time!". Her eyes open wide and she says "No, I'm your son's maths teacher"...