Apparently you know an amazing collection of rude, insensitive people. It's your duty to correct them, make them more habitable for the universe and there's an easy way that you've always got with you. IF they feel they can make sort of demeaning, personal criticism, then they've extended to you the invitation to make your own comment about them. And why not? They'll be offended when you match your head with their pot belly. Perhaps look made, annoyed but you need only say, if you feel you have the right and privilege to make that sort of personal comment then I must assume we are sufficiently close that I can make mine with no hard feelings on either side. They may not "get it", perhaps never but they do need to have illustrated for them the give and take of conversation. Equally if they've just commented on how fit you look or whatever, find something of theirs worthy of positive commentary. In the end, it's your head and what's on it is of concern only to you. Also, if you have people like that all about you, get new friends, the old ones aren't even worth a retread.
I was accosted by a student once who asked me if I found it hard to be as tall as I am and as old as I am......some things simply have no answer.
