Sinister Stanley

When a man marries a woman, and proceeds to perform bedroom antics with his wife's sisters, because this guy is void of any kind of moral compass, and/or is just a complete douchebag.

Girl - "I can't date that dude, he's such a Sinister Stanley!"

Girl - "Did you hear about Dave? He totally did a Sinister Stanley on his wife".

Man - "I have so much respect for Brian. He Sinister Stanley'd the shit out of his wife!".