I just think its unreasonable if generally staff is just working through a busy crowd, not being rude and noticeably overwhelmed and you treat them like something at the bottom of your shoe.
This is something I picked on up really quickly when taking kids out to eat is that almost every time I do another family are making rude remarks to the staff. Sometimes the subtle moan of another family and sometimes a scene. I really do not like treating people like crap, I worked in food when I was a teen; as a waitress, in fast food, in the kitchen.. but never had anyone just verbally spit on me like I see when I go out.
Grant it the restaurants I take the kids to are generally pizza hut, pub chains and anything really close to the cinema of choice but without fail I have another woman say to me thinks like:
w: (to me) Why is it taking this long, there are tables to be cleaned off...
me: (tries to just politely smile)
w: (to host) Excuse me we are standing here... how long is it going to be?
w: -swear word- useless.
Or loud people fighting at the wait staff for not having more drink, or something of that nature but loud enough that I and all surrounding tables here it.
Or male partners pointing and yelling at staff