A guy goes to a supermarket and notices a beautiful blonde who waves at him and says hello. He's rather taken back, because he can't place where he knows her from, so he asks,

"Do you know me?"

To which she replies,

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

Now he thinks back to the only time he has been unfaithful to his wife and says, "Oh my god, are you the stripper from my bachelor party that I laid on the pool table with all my friends watching, while your partner whipped me with wet celery and then stuck a carrot in my bum?"

She replies

"No, I'm your son's maths teacher."