As someone who's always been pretty large, I can confirm that a person's size can unfortunately make them a pretty popular target for bullying while they're growing up.
But while I'm lucky enough to have largely avoided any social ramifications for my size after I came of age, it's also true that this hasn't lined up with everyone's experiences. Even putting aside the fact that there's a whole industry dedicated to making us feel inadequate because of our weights, some adults have found that their peers and even entire businesses have treated them differently once they gained weight.
With all of this in mind, it's hard to imagine that someone who makes a crack about their romantic partner's weight could possibly think they're in the right when they tell their story about it. But a surprising number of people who might've agreed surprised even themselves once they got the full picture.