Off to the side here: Yes, a comment to anybody along the lines of "your style sucks" just doesn't fly. It's not an honest comment, if you think about it. It's saying what you honestly feel an impulse to say... but it's an emotional dump. It's making someone else responsible for how you feel. Honesty itself precludes that 100%.
If a person owns their feelings, it changes everything. Admitting they have poison eye for certain things, personal connotations, etc. Then it's just a response to be considered - as opposed to an emotional snow-in you have to dig yourself out from.
I suppose one important thing is to evaluate outfits by the wearer's own standards, goals, needs. Like, I could go around telling everyone they need to wear miniskirts as aprons and spirit hats (a stuffed animal on their head) to be cool... and obviously, I'd be right because I am the authority on these things... but ya, c'mon, that's ridiculous. Not so obvious, but also not useful, would be suggestions for me to take the teddy bear off my head. To tone it down. I can't do anything with that.
But there is a caveat: If a person is going to the North Pole, they really have to have a puffer. Things like that. No matter what. Sometimes you have to dress a certain way to achieve what you want and that can be depressing, but that's the way it is. Your mother - and your friends - are allowed to remind you of this.