I have had many black cashiers in the last 15 years or so be noticeably chilly towards me after being chatty with the black person who cashed out ahead of me.”
Yes it happens. And white people often act the same to blacks.
Everyone does it on some degree. It is simply a fact of life. When you’re at an ATM at night, I’m sure you’re more likely to let the door open for a white man than a black one.
Blacks do commit violent crime at a much higher rate than whites so our suspicion is warranted. But blacks that aren’t criminals get tired of being treated like ones. Some blacks try to get back at whites by being mean to them. There is also a huge culture of “hate whitey” for various reasons.