This is not a dad joke, but still one of my favorites:
One day Bill Clinton asked Strom Thurmond, "Hey Strom, I've heard you are still popular with the women. At your age how to you keep the wood"? Strom replied, "before I get in bed, I whack it against the bed post three times and I'm good to go."
That night Bill slipped into the bedroom with the lights off and whacked it against the bedpost three times. Hillary shot straight up in bed and said, "that you Strom?"
Strom was known to have a pair that were so pendulous they required “tuck” surgery. I have it on good info from the friend of the doc who performed the surgery. It bothered Nancy when they “frolicked “ in bed.