For The Sake Of My Sanity

 Let's say there was the chick who, during a momentary lapse of judgement, video sexted with this guy one time, and now he won't leave her alone? I mean, hypothetically speaking, of course. And let's say he messages her every hour, wanting to talk to her, and she doesn't know how to block him.

How does she tell him to back the fuck off without being rude?