1. The act of two couples switching partners in the midst of simultaneous sexual congress.
2. Successfully dumping your girlfriend in favour of her sister or roommate.
1. Jane and I were givin er when Jack offered Jill up and we did the old switch-er-oo.
2. Person 1: Yep, as soon as Susan moved in with Sarah, I knew I had to have her, so I gave Sarah the heave-ho and now Susan and I are bumping ugly.
Person 2: Holy shit! You pulled off the old switch-er-oo!