I'm guessing a bunch of 'high school buddies' were not eating in a place like you work for either. More likely Denny's or some local greasy spoon and the staff was the type that responded better to there antics...
I tip according to service. If its 'OK' but nothing special %15. Can go up or down from there. Mistakes happen...Recently ordered cheese steaks in Philly diner. My daughter ordered first and ordered chicken cheese steak. Wife and I wanted beef, but all came out as chicken. She quickly got the corrected order through and got a good tip even though it was her error.