Little Johnny
Little Johnny's mother: "We're going down to see Mrs Jones's new baby, Johnny. Now the baby was born with no ears, but I do NOT want you to mention the ears."
Johnny: "No worries, Mum."
So off they go and see the baby.
Little Johnny: "Beautiful baby. Mrs Jones. How's his eyesight?"
Mrs Jones: Thank you Johnny, but his eyesight's just fine. Why do you ask?"
Johnny: "Well, he'd be stuffed if he had to wear glasses, wouldn't he?"
(Thanks to Maddie for reminding me of this one.)