It's wrong to stiff your friend's on a bill.
Sal was eating lunch with his friend Jake at a diner.
Sal wants to go home.
Sal waits until after he pays the bill to get up and leaves.
Sal leaves the diner before the waiter brings him his bill.
Jake shakes Sal's hand and tells him that he will see him later.
Jake is upset at Sal because he has to pay for his friend's bill.