The Sister Switch (T.S.S)

The sister switch also know as the roomate switch because it applies to roomates and sisters. You find out your girlfriend’s sister/roomate is the more desireable one and you want to switch. How you do it is you suggest a threesome with the sister/roomate to your girlfriend and she is so appauled by the idea she kicks you out. She later vents about to the other and she is secretly flattered why giving fake sympathy. You wait until you girlfriend is at work and you call the sister/roomate. You get past the awkwardness then you ask her out.

There is an alternate scenario where your girlfriend is into it and the sister/roomate is too. In this case you either are very lucky or offered to aide in incest where you are expected to decline.