When to keep your mouth shut

A chap was standing in a queue at the super market till & this rather dishy blonde starts to wave at him & says hello, she looks familiar & he's rather taken aback by such a looker.

He says, "Sorry but do I know you?"

She replies "Well I could be mistaken but I thought you could be the father of one of my children."

His mind races back to the only time he had been unfaithful & says "Your not the strip-a-gram I screwed on the pool table with all my mates watching & one of them whipped me with a bunch of wet celery and stuffed a cucumber up my arse?"

She said, "No I'm your son's maths teacher!"