I guess I just don't understand why a comment like that has to be "insulting" or that they're something to be offended by. I suppose it's kind of clueless, but people are just giving their opinion or commenting on your looks. So what? If somebody tells you look like a certain "random celebrity" I think a perfect thing to say would be "I don't see the resemblance" and then just change the subject. I just don't see the point of being offended or getting mad at being told you look like some celebrity (or anyone else for that matter) I'd just let it go. I'm sure it's happened to all of us at least once. I remember when the TV show The Wonder Years was on, someone told me I looked like Fred Savage who played the main character on the show. I didn't think I did (still don't) and it turned into a bit of an argument all because the other person wouldn't drop it. But it doesn't matter, to me it's one of those things that's "small stuff".
Well, in general, I don't think it's particularly polite to "give an opinion" on someone else's looks, unless you've been specifically asked. It certainly isn't a defense for voicing any and all opinions on others' appearances. If one is going to do so, the onus is on the commenter to make sure the comment is unambiguously complimentary. (Even then, not everyone would consider an unsolicited compliment polite
. It's just much less likely to offend someone than other comments on their appearance.) For example, you probably aren't going to offend many people with "You look great!" or "Your scarf is beautiful." Something like "You've lost weight!" will likely be understood as an attempt
at a complement in USA culture, but many people would be offended by unsolicited commentary on their weight (and the implication that loosing weight was desirable for them). And on the far extreme, voicing an opinion of "You're ugly" is incredibly rude.
When comparing someone's looks to a celebrity, it's going to be very difficult to hit "unambiguously complimentary" unless it's a person you know, and you are sure they like that particular celebrity's looks. Also, I don't really see how saying someone looks like [insert unattractive celebrity] is complimentary, even if said celebrity has many wonderful (non-aesthetic) qualities. If the point is that they have, e.g., the charisma of [charismatic celebrity], then that has nothing to do with them looking
like the celebrity. The obvious, face-value interpretation of "You look like X" is that you literally look like X, not that you share X's non-visual qualities.