You're the Father of One of my Kids
Don't read if you are easily offended
A guy goes to the supermarket and notices an attractive woman waving at him. She says hello.
He's rather taken a back because he can't place where he knows her from. So he says, "Do you know me?"
To which she replies, "I think you're the father of one of my kids."
Now his mind travels back to the only time he had ever been unfaithful to his wife and says, "Oh my, are you the dancer from my bachelor party that I made love to in the back seat of my car???"
She looks into his eyes and says calmly,
"No, I'm your son's teacher."