There are some real douchy people who waiters are expected to take care of with a smile; foreigners, families with screaming babies, needy elderly folks who are angered by trivial things, etc.,.
Today's target will be at the top of the heap; business people.
I firmly believe there is a sliding scale of douchiness that most business people fall somewhere onto. They saunter in with their binders or laptops, ignoring everyone around them until it becomes convenient for them to listen to someone else, and just making it seem like there's an aura of entitlement surrounding them at all times.
There are many kinds of inconsiderate behaviors that these jerks indulge in, ranging from the mildly annoying (insisting on finishing a business-related conversation when the waiter or waitress shows up, sometimes in excess of thirty seconds), to the super-aggravating (leaving an open laptop on the table throughout the entire meal).
I once approached the table of a businessy pair, and began explaining their choices for beverages. Halfway through my list, the female business-type of the pair proceeded to answer a phone call while I was talking. Thinking nothing of it, I continued my list, and redirected it towards the remaining patron who was still paying attention. The woman on the phone douchilly put her hand over her phone's receiver, looked at me angrily, and said, "Excuse me! I'm trying to have a conversation!"
In a perfect world, I would have had the job security to not only make a crude and sarcastic comment ("In that case, why don't you familiarize your own-damned-self with our cocktail list, you pretentious cunt?"), but to take the phone from her, cover it in buttermilk batter, and throw it in the nearest deep fryer. And light her shirt on fire.
If you go out to dinner, don't be a douche. Leave your laptop at home, put your phone on silent, and please understand that you are not the only table that your waiter has. At most, a waiter can spend about thirty seconds at a table on a busy evening, so you should let him or her say or do what they came to do, listen patiently, and continue your conversation after your server leaves. It's not hard, it's just mutual respect.