Why do some guys mistake friendliness for flirting?

I might be smiling but it doesn't mean I like you. I'm just trying not to be rude. Then they'll ask if I'm single and if they can have my number. I just feel so awkward about it.
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+1 y
It's kind of ridiculous. If I smile, they think I'm flirting. If I don't, they think I'm being uptight.
Why do some guys mistake friendliness for flirting?
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