That's how you get AIDS
Metaphorical phrase describing ANY type of risky behavior, be it physical, literal, figurative, or metaphysical. The representation of a disease emphasizes the magnitude of the risk.
*Friend picks up a piece of candy from restroom floor.
"Ewwwww, nooo, that's how you get AIDS!!!!"
"Ewwwww, nooo, that's how you get AIDS!!!!"