Is it a crime for skinny people to workout?

Whenever I say I need to workout or that I'm going to workout, people look at me crazy. They always say, "what are you working out for? So you can disappear." It's so annoying. I'm just working out to tone up my body. I'm skinny but that doesn't mean my body is in good shape.
Is it a crime for skinny people to workout?
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