When a couple gets together, they alienate all their existing friends so they can spend all their free time with each other. As the time passes, the couple slowly lose their friends by always hanging out with each other. In the end, they are no longer part of a circle of friends, but rather a line that connects them to each other.
The term was coined off an actual couple named Mai and Bryan who are still sucking each other's faces off, much to the dismay of the people around them.
Ben: Hey, want to go to the movies?
Sally: Sure, why not. Who do you want to invite? Alice?
Ben:Oh.. well Alice and I don't really chill anymore, ever since she met Bill.
Sally: What happened?
Ben: She pulled a Mai and Bryan.
Sally: Oh, I see. Her loss.