hair to grow on the palm of your hand
A guy gets told he'll grow hair on his palms if he keeps jerking off, and he immediately checks his hands like a fool, making everyone laugh their butt off.
My cousin was told that by his uncle and started flexing his hands like he was showing off at the gym.
My friend looked at his hands like he just discovered he had a third arm.
He checked his palms so hard, he probably got a blister.