Sex joke «Father, father...»

This guy is in line at the Super Market when he notices a hot blonde
behind him has just raised her hand and smiled hello to him.
He is stunned that such a hottie would be waving to him, and although
familiar he can't place where he might know her from, so he says "sorry do you know me?"
She replies "I maybe mistaken, but I thought you might be the father of
one of my children!"
His mind shoots back to the one and only time he has been unfaithful,
"Christ!" he says "are you that stripper at my bachelor party that I had on the pool table in front of all my friends, while your partner whipped me with some wet celery and stuck a cucumber up my ass?"
"No" she replies, "I'm your son's English Teacher"