Crazy People (1990)
When the bus driver (played by David Paymer) appears and says "I need one of you now", after Milo has completed his earthly task of returning the stamps - he says "Hello!?" - this is a reference to his character in Crazy People (1990) in which he plays a mental patient called George whom only says the word "hello".
Sarah Silverman says that Crazy People is highly underrated as a funny movie.
Shawn asks Holloway if he has seen "Crazy People."
"Hey, up yours, pal! I've got a package to deliver!"