I can't think of anytime I've left no tip. I have left a restaurant though before even ordering. Went to a chain place near home, got seated right away. We weren't right by the kitchen, but we were in the main aisle where every waiter/waitress/manager going to and from the kitchen had to go by our table. We sat their for 20 minutes, with menus, and not a single person acknowledge us. As we left, the hostess, and I know it's just habit, says "Have a good night". Didn't say anything, we just left. Haven't been back there since.