Switch Mack
When you're macking on a chick for awhile and then get introduced to her hotter friend/co-worker/neighbor/sister. You then decide to go for the other chick instead, switch mack style.
man, I was out at the bar last night and was macking on this cute chick, only to be introduced to her tasty roommate later in the evening. I pulled a switch mack on that shit and ended up hooking up with the roommate.