Coffee is Like a Mistress

Today while I was at La Prima Expresso's and ordering a cup of milk:

(Cashier rings up the register for a 16oz coffee and 1 chocolate croissant.)

Me: Oh, I got milk today.

Cashier: Oh, I'm sorry… let me ring you up again. Also, that's really strange. You usually get coffee.

Me: Yeah, but coffee is like a mistress—you do it often enough, you end up having to take a break from it sometimes.

Cashier: That's the oddest thing I've heard today.