Believe it or not, most people know everything there is to know about their own weight and "any comment" on it will accomplish nothing but make them feel worse.Unfortunately I've noticed that fat people are easily offended by any comment about their weight no matter how kindly worded or intended.
I have serious trouble understanding the process that leads people to thinking that the 115th "well-intended", "kindly worded" comment about their weight will finally make them see the error of their fat ways and they'll start becoming healthy.