If I've received good customer service, I'm more than happy to tip and tend to give around 10%. If the service has been poor or average (average being they take your order and give you your food but nothing above and beyond in terms of their interactions etc), then I don't tip. I've noticed the unhappy reaction I get when I don't tip but surely their level of service should warrant a tip? And are they not paid a wage aside from tips? Or is it me, and actually tipping in the UK is now the norm and highly frowned upon if you don't?