How would you react if an acquaintance says "wow, you look exhausted"?

Respond with, "I didn't get much sleep . . . "

I don't understand the offense people feel after being told this. If I tell someone, "you look well rested" does that mean I think she is more attractive?

They're just observations. . .

I kinda hate how words like "tired" and "ill" have become insults. If I'm saying you look tired or ill, I'm trying to show concern for you and interest in how you're feeling. It bums me out that anyone could be so consumed by their looks that they take it negatively, but most people seem to be.

The word "sleepy" puts emphasis on the lack of sleep, which is generally better received. Also use the word "seem" instead of "look", or put the statement in the form of a question which they can then confirm or deny ("are you feeling sleepy?").

If I'm actually exhausted then it wouldn't bother me. I have a sleep disorder so I am exhausted quite often. There's no shame in the truth as far as I'm concerned. I sure as hell am not going to pretend I'm not tired when I am.

They would be right there's so much shit sleep backlog that I look constantly drained, exhausted and fucking old even when I've had a decent sleep.

I wouldn't care. I'm told this often.

punch them in the face jk lol I'm pretty much always exhausted so i would just agree.

Well, usually I am exhausted, so it's true.

I usually respond with "Thanks, fucktard."

I'd say "yaaa, I know."

Some people, women mostly, take offence to it because it can also come off as saying they look old.
If a guy wants to make points with a woman, don't ever say this.

when im exhausted im quiet so I prolly wouldn't say anything

This requires me to have a normal nights sleep, even if I did I honestly don't think it would bother me and I'm usually pretty insecure about my looks

LOL. I've been told this before. I laugh it off. People see what they see. That's fine.

I've been asked if I'm angry a lot because I have a thoughtful frowning expression on my face (when I'm thinking).

I don't get offended easily and I only take mental notes on things of an important nature.

It was simply an incorrect observation. Everyone makes those.