We used to go to restaurants in groups after field service or after assemblies, etc.
We never acted rude and as a group always left an appropriate tip- 10-15% or even more gratuity if it was not already included in the overall price.
Anyone going to a restaurant should always leave a tip. Restaurant workers do not get paid much and they rely on tips to supplement their income.
Only in extreme cases of a rude waiter or waitress, should one not leave a tip. And then if the service was so bad, you should talk to the manager in charge.
I always reflected that if one of my family members were working at a restaurant I would want them to receive a tip.......so why wouldn't I leave a tip when I am served at a restaurant.
Ronin1