Everyone who wants to lose weight has to go on a diet. Since most of the people are somewhat overweight, this becomes a hot topic to talk about. Although both men and women go on diets, I will primarily focus this towards the women population as it is more of a discussion topic for them.
When you see someone and notice a weight change, you usually want to mention that they look better or that they lost weight.
Remember that it is ok to talk about dieting with friends, but if you are among people you do not know too well, make sure there isn't somebody who is overweight already. You don't want to talk about dieting in front of these people because they might be self conscious about their weight.