Op, YANBU!! Most people are not doing this maliciously but for some people the subtext is “won’t you be hot in that chubby? If you were slimmer you’d feel happier in shorts/short sleeves etc”.
Anyone who has never been heavier than a size 10 won’t get the nuance of this.
I don’t comment on appearance. I might say “I love your shoes” but I don’t comment on body size/shape or whether anyone has lost/gained weight etc.
I am also careful that if I’m with more than one person, saying “wow you look amazing” to one person makes it very obvious that you’re not complimenting the second person.
I have spent years and years listening to people praising the appearance of people I’m with and not saying anything to me (or, worse, a sympathy “and you look nice too”).
no-one had to tell teenage me that I wasn’t very pretty - the absence of compliments from friends parents, adults generally said it loud and clear.
I feel so strongly about this. I know several friends who are conventionally beautiful but have a sister who isn’t (or the other way around). It’s so hard. “The pretty one and the funny/clever one” eurgh. And not fair on either sister.
OP, I hear you. It is a thing. “Aren’t you hot in that” is so annoying and insensitive.
To everyone who thinks the OP has a massive chip on her shoulder, just don’t say it to someone who’s a bit bigger. Assuming their adults, they’ve dressed themselves the way they have for a reason