This has happened twice in the last month. I've been out with friends for a meal, the bill has come, I've calculated my share and added a few quid for a tip. When the waiter comes with the card reader, I put my amount in and say "that is for a tip as well." My friend has then looked at the bill, deducted my amount from it and only paid the remaining amount! So the waiter gets nothing and I've subsidised my friends meal!
I know I should have said something at the time, but I thought "this is for a tip as well" made it pretty clear to all concerned. Both times I was a bit stunned at the cheek and not sure how to handle it. How can I avoid this in future? I don't usually have cash on me. It's made me pretty annoyed, plus embarrassed that we didn't leave any tip, and I can't believe two separate friends pulled the same stunt.