If the service in a restaurant is SO poor you can always detip.
If they have added the 12.5% service charge you take it off PLUS an extra 12.5%. Remember to explain why you have done it.
If there is no service charge simply take 10% off your bill.
"This food is shit and the person serving it takes bloody ages to do anything, lets detip."
"Detipping... that means more money for booze. Let's do it!"