Why is it ok to make fun of someone's weight??

My husband is a bit overweight. Not too much, but enough to be noticeable. Any time we go to his family events, everyone likes to pick on him. Everyone joins in and it's a good time for them. It's like an ongoing joke with his family. It gets on my nerves every time. Like seriously, why is it okay for them to do this? My husband is not the type of person to speak up, he just goes along with it and laugh it off, but I know it bothers him. He is self conscious about his weight and is really trying to lose it. He has been going to the gym and is even trying to eat more fruits/veggies, which is saying a lot. He is an extremely picky eater.

His family will just bring it up at the most random times. He will just be standing there talking to someone, and someone else will interupt him saying "gosh, Tony, look at that belly!". Or something along those lines. When he goes to sit down, they make comments about him breaking a chair. Like I said, it's not like he's extremely overweight or anything, just enough to notice. It's not like his whole family is fit. Most of them are bigger than he is, and I think that's what bothers me the most. Sometimes I just want to chime in and say "look who's talking". But I never would, because I won't stoop down to their level.

They all like to pick on him about anything. When he was in school, he struggled and it seemed like he wouldn't go very far. He is now one of the very few in his family who is actually doing something with his life, but they all act like he is the same trouble maker he was in school.