A "friend" of mine tried hooking me up with the hugely overweight chick (5'6, \~325lbs). I told her "Sorry but this isn't going to happen" and when she asked me why I said, only this, that she is "Too big for for me." She proceeded to say Fuck you and I hope you die. I said I hope you find someone that makes you happy. 

I know I could have been nicer about it, but I felt the right thing to do was being transparent with my reasoning. I am allowed to have a preference of non-fat people and if they ask why me, I believe it is justified that I don't sugarcoat shit and give them my truth.