Well
I just woke up from my afternoon nap. I never put a tip on my restaurant bill.
Two reasons.
I don;t want the person who waited on me and gave me excellent service to have to share what they earned with a bunch of other employees and I simply want that tip to be cash so its not traceable.
I usually just find my waiter or waitress after I have paid the bill and give them cash quietly and always more than what is UCR. They work hard and put up with a lot of crap from people and they are trying to make a living also..