The HAC Rule primarily applies to Friends With Benefits (FWB's), occasional hook-ups (OHU's), and one night stands. It protects all parties involved from given consequences of the following actions:
Any party that violates the HAC Rule is subject to the potential suspension of their FWB or OHU status, or the potential for the One Night Stand to become one of the former status'.
Beth: Ok Mike...I'm really drunk, but that doesn't mean the HAC Rule isn't in effect. I have a work meeting tomorrow and can't have any marks left on me.
Mike: Of course...but does the HAC Rule really need to be in full effect?!?! Shouldn't it just be the H & C...I mean, you're not planning on showing your ass, are you??
Beth: Does that mean you want to be exclsive?
Mike: Uh...ok...HAC Rule is in effect.