Basic Trope: Good people treat service personnel well, bad people treat them poorly.
Straight: Alice goes to a speed dating event. While there, she notices that Bob speaks politely to the waiter, takes his suggestions, and tips well. Conversely, Dan berates the waiter for imagined slowness, questions the man's knowledge of French cuisine, and doesn't tip at all. When she dates the men separately later, Alice discovers that Bob is an overall decent person while Dan is an unrepentant jerk.
Alternatively, "Nice to the Patron". In a didactic work aimed at the lower classes, Bob and Dan are waiters. Good Bob is properly servile and treats customers well; evil Dan is insolent and slow to come to the table.
Alternately, Bob and Alice are getting very poor service from their waiter. While Bob is quite willing to generously tip any server who actually works hard and earns it, he's also ready to berate anyone who deserves it.
Double Subverted: But only to protect the waiter from an assassin's attack while preventing the killer from realizing Bob was on to him.
Bob misunderstands the concept and is only nice to waiters, no one else.
The establishment enforces a 50-dollar "asshole tariff," and the waitstaff offer back rubs and/or free beer to the nice guys.
Zig Zagged: Bob is usually nice to service personnel and his "social inferiors", but sometimes is horribly rude to them, seemingly without a pattern; in his main storyline, he's stuck in the Heel-Face Revolving Door.
Averted: Everyone treats service personnel the same way, regardless of their moral or ethical standards — the story isn't about "the little people", after all.
Enforced: The writers want to establish a new character's personality traits (especially if they're unpleasant) before they formally meet the main cast, so they're seen in a restaurant or other service situation.
Lampshaded: "They're holding another big 'meet-up' event here at Chez Snooty, so we can expect most of the customers to be extra nice tonight to impress their dates."
Invoked: Alice has all her first dates at restaurants specifically to check out prospective boyfriends' behavior.
Exploited: Bob is extremely nice to the waiter; so nice, in fact, that the waiter looks the other way when Bob puts something in Alice's drink...
Defied: "Politeness to one's inferiors is a sign of weak-mindedness and moral turpitude! If they deserved better treatment, they would have been born into the upper classes!"
Discussed: "I knew Dan was going to be trouble when he corrected the waiter's pronunciation and called him a useless pig."
Conversed: "The heroes on this show are all really polite and well-mannered to the servers when they go to a restaurant. See, even when a fight breaks out, Bob makes sure the waiter doesn't get injured."
Implied: Alice tells her friends about breaking up with Dan over dinner last night and leaving him for the much kinder Bob.
Deconstructed: Since the concept of Nice to the Waiter is well-known, anyone who cares about their reputation can simulate it to create a favorable first impression. Thus it's not always as good a test of character as one would assume.
On the other hand, it's very difficult to keep up the pretense of being Nice to the Waiter if you aren't used to it — many phony "good guys" will revert to their normal Jerkass behavior quickly if something goes wrong with their order.
Furthermore, it can quickly become apparent if someone is a genuinely decent and respectful person, or if they're just pretending to be.
Now that you've finished, I'll bring your check and you can go Back to Nice to the Waiter.