[not american] i've always wondered about that. is it they feel uncomfortable because the person is wearing something normally associated with gangbanger/dodgy person.

would it happen if the person was dressed like whatever the stereotypical white person business casual attire is for the area?

i just can't see somebody being uncomfortable __just__ on color of skin. there surely has to be something else which triggers it.

person acting sketchy (maybe because they feel out of place rather than being up to dodgy activity?