I forget the name of this manga...?

I was reading this manga.. and I totally forget the name of it.

Okay, all I really remember is this REEALLY fat girl confessing to a guy, and of course, he rejects her cause she's just so ugly. I think she beats him up after that (the girl MIGHT have flashed him and she has a birthmark on her thigh I think) . And then, with his ego smashed he decides to join the boxing club. But as it turns out there's only girls in the club, but they let him join anyways. And so, there's this really pretty and skinny and not ugly at all girl there, but it turns out she's that fat girl he rejected before. (she decided to join the boxing club and got skinny after she got rejected.)

Does anyone know which manga I'm talking about? o.O