Tip the pizza delivery boy

A college pizza delivery boy arrived at the house of Larry Johnson. He delivered the pizza to his trailer. After giving it to him, Larry asked: "What is the usual tip?"
-
"Well," replied the youth, "this is my first trip here, but the other guys say if I get a quarter out of you, I'll be doing great." "Is that so?" snorted Larry. "Well, just to show them how wrong they are, here's five dollars."
-
"Thanks," replied the youth, "I'll put this in my school fund."
-
"What are you studying in school?" asked Larry.
-
The lad smiled and said: "Applied psychology."