Americans tip 25 to 30% ? That is outrageous, here the normal tip amount is 10 to 15 % , except for exceptional service, then 20%.
I do not tip more then 10% if service is poor, and if the service is horrendous, and I see no mitigating factors( restaurant is crowded and I can actually see the staff struggling to keep up) then I might tip less. I normally tip 15%.
People who overtip so - so service are ruining service for the rest of us, cut it out!!
I don't mind an automatic tip of 15 % for large groups since some people are cheap and don't throw in their fair share of tip,and then those of us who do have to throw in extra. I would expect decent service though. I understand some things going wrong though, and I am not heartless. If it is really busy and the restuarant appears understaffed I don't punish a waiter or waitress who is really trying to keep up.