Once a waitress I worked with stormed after a party who just left her some change and threw the coins at them screaming “Keep It! You obviously need it more than I do.”
Needless to say, she was canned on the spot.
Unless they only had coffee leaving just change is pretty rude. Unless it was an elderly couple or disabled on fixed income, in that case I wouldn’t hold it against them. But everyone knows with dining out, unless its fast food, one is expected to pay the server a little something as that is how they make their money, whether it’s right or not that is the way it’s set up in the US.