When a woman lies to a man about finishing her menstrual cycle in order to coerce him into sex. Either upon completion of, or during the act of sex it becomes clearly apparent that the woman is in fact still menstruating by the blood spatter visible both on the man, and on the surrounding area.
A direct reference to the TV show Dexter where the main character works as a blood spatter analyst with a severe dislike for evil-doers ( in this case lying women).
You dextered me!
I got dextered by my girlfriend last night.