A solo sex act where a male heats his scrotum with a hair dryer or similar impliment followed by "dropping" in a bowl of ice water to introduce rapid temperature change. This results in the testicles shrinking (shrinkage) and if done properly, a "hands free" ejaculation/masturbation.
Dude! My roomate was trying Joy Dropping and burned his nuts with the hair dryer! That idiot needs a real girlfriend...