A Manhattan Moodswing begins when you are fucking a girl in the ass and you sense a sudden mood change for no apparent reason. You then lift a nearby cinder block over the girl's head and knock the bitch out. You then flip her over and start doing her hardcore in her limp vagina.
Haidyn: Zoie, what the hell is that on your head?
Zoie: I'm not sure, but I think I received another Manhattan Moodswing.
Haidyn: Damn, he knocked you the fuck out.