An arbitrary threshold of arousal, which once passed, will cause an individual to engage in behavior which may be risky to their freedom, health, bank account... or all of the above.
Commonly observed in news reports about dentists who abuse their female patients while under anesthesia, teachers who strike up affairs with underage students, etc. The negative repercussions of a triggered perv switch can oftentimes be avoided by channeling the energy into a jack attack.
Dumb-ass completely flipped his perv switch, now he's looking at 5 to 15 years in a pound-me-in-the-ass prison.