For me the way people treat restaurant staff reveals a person’s character.
Customers who treat waiters as ‘slaves’ or ‘servants’ … I consider them as the ‘scum of earth’ and not ‘kings’.
A man (or woman) who, for no reason, is actively unpleasant to waiters .. my advice is to avoided them. Also those who patronize waiters and other service offering staff. People that treat waiters as though they were invisible … are all cretins! They think that it is a sign of sophistication … NOT!