Any waitress/waiter should smile when serving people. I have to admit that if they dont smile and they are white the first thing that comes to mind is that they are a racist/bigot. Usually I can get them to smile and talk about themselves. If they never thaw out I assume they are racist.
Then you're employing a fallacy, because you don't have a basis for that conclusion. They could be tired, bored, having a shitty day, or just not a smiley type. Some of that might be unfriendliness too, but their white customers are gonna get the same thing, so there goes that theory.
But "show ALL your teeth", SMFH. I've sat down to a
lot of meals in a
lot of restaurants in almost all 57 states, and it's never once occurred to me to count somebody's teeth. Ever.