You can truly judge a person's character based on how they treat a person who can do nothing for them.

Never mess with someone who handles your food.

A person who is nice to the waiter but is not nice to you really doesn't like you.

"If you want to know what a man's like, take a good look at how he treats his inferiors, not his equals."

The waiter is there to serve me, not to gather compliments.