I bet you don't wear overalls, a dirty baseball cap and Redwing work boots to work. Do you? Why don't you? Because you'll look like some ignorant hick that can barely write his name, not the chief of staff for a state legislator. Appearance is everything in our society.
If you see some white dude in overalls, dirty boots, foo-man-chu mustache, probably dipping snuff and a greasy baseball cap, you're going to automatically sterotype him as a racist redneck and treat him differently than you would someone else presenting themselves in a different way. And, please, don't insult our intelligence and say that you wouldn't, because we all know better.
Everyone is prejudice. Libbos do more to keep prejudice and racism alive than any other group in this country.