It's rude not to tip a server
Tim is in a restaurant after having paid and a waiter has brought back a tray with coins and offers Tim his change back.
Tim wants to respond to the waiter's offer.
Tim declines to take any money out of the tray and thanks the waiter before leaving.
Tim grabs the tray and slides all the coins into his hand, thanks the waiter and leaves.
The waiter is happy to receive more money and happily walks back to the kitchen.
The waiter is disappointed that he's lost out on potential earnings and is angry at Tim's lack of understanding about how it all works.