What does it mean when a guy calls a girl scary?


I am pretty quiet and shy. And naturally I don't smile. I've already overhead two different guys say that I am scary. And neither of whom know me that well. Am I ugly? I don't think I look mean. Maybe serious? At work I've been told that I look like I'm a little high strung or stressed.
What does it mean when a guy calls a girl scary?
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