There are too many "favorite" ways to be ball busted to list.
I think squeezing by hand or in a humbler type device rates high.
Dropping heavy objects after trapping the testicles at the bottom of the scrotum. This can be a toilet seat of cover or an object.
Continually hitting the testicles with a solid object or a mallet, or a hard ball on a dowel.
Compressing the testicles in an ace bandage and restricting access to them so you can't remove it as the pain builds.
Just a few thoughts