Ok, this is sack busting more than ballbusting, but here goes.

1. Mix a thick paste of chilli powder and warmed massage base oil.
2. Rub vigorously into scrotum and external skin of the penis for two minutes only.
3. Wash your hands.
4. Cuss me because nothing is happening.
5. Muffle that yell.

Five minutes and gallons of cold water later, plan to do it again.

Disclaimer: chilli powder varies greatly in strength, as do pain thresholds.
Don’t come crying to me if you injure yourself.