A guy goes to the supermarket and a beautiful blond woman waves at him and says hello. He's rather taken aback, because he can't remember where he knows her from.
He says, "Do you know me?"
She smiles and says
"I think you're the father of one of my kids."
He is, of course, stunned. His mind reels back to the one time he was unfaithful to his wife.
"You're the stripper from my bachelor party? I remember. We had sex on the pool table while your partner whipped me with wet celery."
She smiles and says,
"No. I'm your son's math teacher."