When your balls get so sweaty that your penis and scrotum stick together. Ca- (cock) -bal (balls). This usually happens while outdoors for an extended period of time, then transitioning into a cool, air-condioned area.
Riding in your car that has no air then going into the movies.
Spending the day in the sun at your Grandma's July birthday BBQ then going inside, in the air conditioning, to sing happy birthday to her around her cake.
Guy #1: "Dude, it's so hot out today."
Guy #2: "I'm sweating so bad I have cabal going on down south."