When you purposely give your own erect penis an indian burn.
I gave myself a GeronimOUCH! so bad, that my cockskin started to split and bleed.
What sky-divers yell when they jump out of an airplane at an altitude which is too low to allow their parachutes to open, but too high to keep the sky-divers from becoming the pizza sauce on an upside down parachute pizza.
As Scooter jumped out of the airplane 187 feet above the ground, he yelled, "GeronimOUCH!"