It's funny that fat girls never ask if they're fat...
HAHAHA! It is funny because it is so f_ing true! ya, its like a catch-22: if you are fat, you know it and would NEVER talk about it; if you aren't fat and you ask, you have no confidence or are trying to get somebody to notice you.
Well, generally I think that the best solution is to say as little as possible about it, say "no"(look honest) and change the subject as quickly and smoothly as possible. I don't think that joking about it is the right thing to do all the time, not the time for CF because the girl may think that you are trying to evade. But, and there is a butt, if you have a really flirtly jokey atmosphere with the girl try some of the suggested lines and try to step up the kino to show that you like what you see, that will lower her defenses with the joke and bulid up her confidence with the kino+reassurence.
Ave