BMI, straightness of teeth, smoothness of face, relative size of nose, etc, etc, etc.
It’s a personal opinion. There are no rules for what constitute prettiness or ugliness. Some people think fat people are more beautiful than thin. You can not determine beauty by how wide the nose is, nor how smooth the skin is.
Would you say there is no bad tasting food,?
Yes, I would say so. All food that Hashem created is good (except if it’s bad for your health). A food can taste very sharp, very spicy, but bad? That is in a person’s personal taste. And I think we should all appreciate all the food Hashem gave us, and not call food bad. I don’t like liver, that doesn’t mean it tastes bad. Other people think it is delicious.
If you call a person ugly, there are others who might think that person is beautiful.
To call a person ugly, is an ugly think to do (even if it’s not to their face)
P.S. I know a few people who don’t have nice straight teeth, and they are gorgeous.