@alyx @thor in most cases, the wait staff should be attentive; usually a little too attentive, but they get better tips by trying to kiss ass so they overdue it, and you don't actually have to try to get attention unless you need something in the middle of a meal when they dont expect you to actually need anything.
and at that point, you politely wave or call out "excuse me when you get a moment..." while they pass your table by to assist someone else.
we aren't total assholes, but the assholes do exist (and usually tip like shit) so the moment wait staff realizes a person/group is that rude and disdainful towards the wait staff, that's when they purposely start ignoring you, or disappear into the kitchen for lengthy periods, or do something else passive aggressive. and at the very least, you can be damned sure the waitress/waiter you pissed off has already bitched about it to all the other wait staff and probably the kitchen so the integrity of the rest of your visit to that establishment is endangered.
you won't notice it, but they will spit in your food or do something else to it.
it's the rude people trying to act more important than they are that do the finger snapping shit.
feel free to bitch-slap anyone who actually does that in a restaurant.