There was a piece recently on tv, might have been the 7 o'clock show, where Dom Littlewood filmed the reactions of the public to his 60-something sound engineer asking them the time,directions etc., first in just t-shirt and jeans and then with a hoodie, with the hood up. The difference in the reactions was quite startling.

You can say "don't judge a book by its cover" and that you can't generalise over a whole group of people as much as you like, but human nature is to do just that and judge people by the first impression. I'm not saying that it's right or wrong, but that it takes significant effort of will not to jump to conclusions.