Murder Mystery Theatre

Having sex while you're menstruating, or having sex with a woman who is menstruating. Specifically describes the situation of having sex in the dark, and not noticing the condition until turning on the lights or walking into a lit room after the fact. Indicates surprise of noticing the site of your passion is splattered with blood, much like a murder scene. Situation is amplified by white sheets.
Can be expanded to "Murder Mystery Dinner Theatre" to imply that oral sex took place.