At a full service restaurant, 20% unless they really did something wrong.
You are generally talking the difference of $5 or less between a 15% and 20%. Most of the time, you will be wearing a watch worth more than that person makes in a month. You want to look like a cheap piece of s*** over a dollar or two? Considering tipping less than 15% at a full service restaurant? They better have dropped a plate of food in your lap.
FYI- most restaurants have a tip split policy, some do it voluntarily. Bartender gets 20% kitchen 10%, server 70% is fairly standard.
Also, as mentioned, we have a “server minimum wage” here in the US which is far less than for other jobs. In some states it can be as low as $3.00/hour. You can debate the ethics of that but it’s reality and your “protest” only hurts the person doing the work.
Baristas, cab drivers, doormen, etc …. If they go out of their way, or do something extra, tip them. If they do the bare minimum and just get the job done, don’t.
There is a lot of overtipping requests, don’t get me wrong I hate seeing it on the swipe-screen everywhere too. Just don’t take it out on the good folks working in restaurants.