He's rather taken aback because he can't place where he knows her
from.
So he says, "Do you know me?"
She replies, "I think you're the father of one of my kids."
He thinks back to the only time he was ever unfaithful to his wife.
He says, "My God! Are you the stripper from my bachelor party that I laid on the pool table with all my buddies watching while your partner whipped my butt with wet celery and then stuck a carrot in it?"
She said, "No, I'm your son's math teacher."