I hate it when people do this... Mostly because I don't have a strong emotion like the one they're describing, and the less I feel the emotion they're trying to put on me the more annoyed I get.
I usually don't pay too much attention to how I feel, but when someone f.ex. says I look happy I might acknowledge to myself that I might feel somewhat happy, but as others have said that mostly makes me want to hide it, since someone pointed it out.
My boyfriend has a bad habit of pointing out that I look thoughtful almost the second I happen to dare to let my mind wander, that seriously pisses me off and I have told him as much, I just hope it will stick.. 
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Self-diagnosed aspie, currently pursuing official diagnosis.
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When in doubt, drink water.