What if someone calls me fat and/or ugly -- what should I say?

Say "Wow, aren't you so observant?". Yes this is a hard one to do when people say hurtful things, but it has a nice shock factor. You can't let your voice waver at all if you choose this option. Or, ask them why they think that and what makes them think they are better than you. Chances are they will flounder and won't be able to come up with a good response, making them look foolish. You can also compliment them offhandedly and get a similar effect. Such as, "well you are so pretty, but your personality dresses you up in ugly". The best way to handle these kinds of people is to make them think you don't care what they think. Even better when you actually do stop caring and focus on more important things in life.