Friend of mine went to pay a debt in cash, they refused to take it, he was relieved of the debt in court as they would not take his legal tender
It it one of those places that takes a 'House Cut' of the TIP that I want the wait person to get, then I give it to that person in cash.
The only problem with tipping a server directly is that the establishment may have a policy against him/her accepting tips and him/her may lose their job if caught. I've seen this happen.
Didn't mean to make it controversial. Just joining the topic. I will admit that having a twenty tucked away in he wallet can be handy
When I was still a teacher, I once told my students that I kept a $100 tucked away in my wallet in case I got held up by someone who had a pistol shoved in my face. I was going to hand over the $100, and hope we both parted HAPPY!