The balls that women freeze off when they climb into cold waters. Women don't have testicles so we need something to freeze off besides our breasts because that would be saddening for both sexes. The moment when you get your groin area submerged into the water and you must stop and breath those are your theoretical testicles falling off.
When she cannon balled into the water, you could see her theoretical testicles shrivle and fall off.
It's complicated; When you cum on or near the hair on your crotch, don't clean it up, and you do not take a shower in a day, you get tropical testicles. This also occurs if you cum, don't clean it up, and engage in exercise. It gets its name by the tell tale sign of this ailment; Hot, humid crotch stink.
Jonathan: Yo dude come check this out!
Michael: No way, I can smell your Tropical Testicles from here!