What is something that is considered socially acceptable if you’re conventionally unattractive but socially acceptable if you are not?

I thought of this after seeing the popular opposite question.

As a guy, I’ve noticed I can compliment younger women if they are unattractive without them thinking I’m trying to flirt. If a girl is attractive, I can’t say I like their sweater. They always would get annoyed. But I like to compliment people.

So I’ve noticed I can get away with complimenting anyone who doesn’t expect me to be attracted to them. Guys, older women, overweight women, etc. And they genuinely appreciate it rather than getting offended.