This is something I've always struggled with. I know that they invariably think I'm older than I am, because I've never told a person my age and had them not respond with surprise at how young I am. Generally, I can't judge what people think of or feel for me unless they tell me. Conveniently, I moved last year, and a number of the many people I have met since then have been surprisingly vocal in expressing their impressions of me.
Three people have called me "serious." Three have called me "a weirdo." Two have called me "shy." Three have called me "confident." Four have called me "intelligent" or "really smart." Two have expressed surprise at the apparent dichotomy of my personality (a serious, reserved, intellectual woman who also collects NES games and decorates her apartment with Wolverine Pez dispensers). One has expressed surprise at a different dichotomy (me seeming shy and timid but turning out to be very self-assured). Two have called me "attractive," one of whom also called me "amazing," but he was rather drunk at the time. One has called me "an alien." One has called me "nice" and "kind." One has called me "sweet." Two have called me "a positive person." One told me that I give off the vibe of some Zen monks she met--that's my favorite.
Ironically, it was a boost to the ego, which immediately served to disprove her point.
I'm sure there's been more, but that's all I can recall at the moment.
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"A flower falls, even though we love it; and a weed grows, even though we do not love it."