I'm trying very hard to understand, please help me GWS. What is the difference between discriminating in...?

You can have your preferences but there is no excuse for the lack of manners you showed to that cashier. I don't find a lot of people aesthetically pleasing,but I don't go out of my way to be rude to them just because of that. Don't you get it,it's not your preferences everyone has a problem with,but the way you treat people who aren't up to your standards.