After having been very publically shouted out by a restaurant owner because, I suspect, of my accent (English) with the line 'Here we tip, we are not cheap' because I left 0 on the CC slip (and had put the cash under the side of the plate on the table instead as I normally used to do, because I know too many places that stiff the staff on CC tips), I will no longer tip cash when paying on a credit card. I have never (and will never) go back to that place, and will always add the percentage to the cc now.