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If a man decides to not jack off for a very long time, an abundance of semen will collect inside the testicles. Once the semen level reaches a certain point, the testicles will combust.
Kid 1 - Yo man you been jackin it?

Kid 2 - Nah dude I stopped doing that shit

Kid 1 - Watch out for testicular combustion!
by ajay69 June 29, 2011