Why do our aunts call us fat?

My sister and I sometimes visit our cousins house. Our aunts are there most of the time. Tell me why weight always seems to be one of their main choice of topic. The first thing we hear coming from their mouths are, "You've gained so much weight!" .. "You've gotten fatter from the last time I saw you.".. They're touching my sisters calves saying they're huge. My sister and I are 19 and 16. I personally believe that this is the age where we begin to take everything to heart.. when someone says we're fat or we've gained weight..obviously we're going to feel like sh-t and want to stop eating. Not to mention, a couple months ago, I was on this "diet" sorta thing and that was when they didn't call me fat... in fact, I think they even mentioned that I've gotten skinnier. But since then I've been eating a lot and just came back from a cruise..and sub consciously noticed that I have gained weight..just didn't want to accept it. But it seems my aunt has already confirmed that fact..... Because of this, I've decided to go back on that "diet" and go back to my skinny self. I see it as a motivation now sort of. I want to go back to my cousins house and have my aunts see that I'm no longer "fat". But I'm just really curious to know why aunts are usually so judgemental? Aren't they aware that calling someone fat is extremely rude and insensitive?