As a waiter, single men were so-so.
Single women were bad.
Black-Americans are notorious for low tips.
Even black waitresses hated to wait on black parties.
When we'd catch a party of 12 stealing food by ordering ONE plate for the salad bar, yet passing it around so everyone could "fill up", the screams of racism could be heard for miles.
Notice how few Sizzlers are around these days.
You simply will go out of business if you have a predominantly black clientele.
Yeah, whitey was bad to blacks 60 years ago.
But food isn't "free", not now, not then.
What about Bikers (motorcyclists)?
Personally I’ve always left at least 20% if the service wasn’t exceptionally terrible.
I have seen Mom & Pop restaurants in one stoplight towns get real quiet when several of us walk in wearing typical Biker gear. I guess I try to kill the negative stereotypes by leaving a respectable tip. Those I ride with usually do the same.