I was taken for lunch and the person paying emptied their coin purse onto a plate as the tip - the amount was fine, probably about a tenner in loose change for a £70 meal, but I thought it was a bit crap for the waitress to have to carry loads of 10p and 20p pieces (and some pound coins) around in their bum bag for the rest of their shift. I did raise an eyebrow and they (the person paying) said they thought it was fine as long as the amount was ok.