My brother, uncle, mom, grandma, me and our kids went out to dinner once where they automatically add the tip to the bill for parties over 6 and the waiter stiffed us and did not show up after serving our main dishes for 45 minutes... Mom and grandma wanted to warm up their coffee and we could not find our waiter anywhere (he ditched outside for a smoke)...
After a while of not being able to find him, I took it upon myself to get up and go to the kitchen and get the pot of coffee myself for them...
Mom and grandma argued with the manager for a half hour to get the automatic tip removed from the bill because the service did not deserve it... The manager finally caved in...
When it gets so bad that you have to resort to serving yourself, they do not deserve a 15% tip... they left him only like 5% and said that's all he deserved for not following through with the post main dish service...