A joke from many years ago:

A man who doesn't travel much takes a train trip, and after the porter helps him with his luggage, the guy asks shyly:"Umm.. my good man, I am not used to this... what is the average tip people give you?"

Porter: "Oh, about $5, suh!"

Guy gulps hard and reluctantly fishes out $5 and hands it to the porter.

Porter: "Why, thank you, suh! You are the first one in 3 years that's come up to the average!"