To go behind your best friend back to start dating his ex. Works best when the best friend has only just broken up with said ex. A Mikey will not mention anything to the best friend, he will simply start rooting the ex. This ends in the Mikey and the ex dating.
Person A: Did you hear about X and Y?
Person B: Yeah, way to Pull a Mikey on old Z.
Person A: Poor Z, he and Y had only just broken up.