I ate at a restaurant in Las Vegas and had horrible service. The waitress took our order (we ordered drink and food at once), brought our drinks, someone else brought out food, and the waitress brought us the check. We saw her three times. The hostess, in between seating people, was running around like mad trying to take care of tables and service. When I left, I asked her if they split tips and she said no, so I gave her the money. The waitress got nothing.
I'll tip if service is adequate, or even lower than that. Otherwise, it's not happening. Tipping is the server's way of earning money, and I see poor service as an indicator that they don't need money.