If someone said to you, "Why don't you pluck your eyebrows?", and you answered, "Why would I?", and they said, "So you can be pretty", how would you feel? Was this person being rude, even if they didn't mean to be?

Yeah, this person was being a bit insensitive. I wouldn't say rude necessarily since they didn't intend to be that way, but they weren't being very considerate or sensitive to what they were saying. People say stuff like that all the time though (not the eyebrow thing specifically but things that are kinda rude and insensitive) so I wouldn't worry about it. They're not trying to insult you or make you feel like an unworthy person so I wouldn't take it too personally. But if this person keeps saying rude and insensitive stuff, it's best that you avoid them. It's hard and kinda embarrassing to be around people like that, even though you know they don't want to actually hurt you.