There's mutiny in the air. Also Viennese dark roast, but mainly mutiny.
Pirates, like the one working at the cash register, often would mutiny if they felt they were being mistreated by their captain; you can say that there's a broad consensus a a mutiny is coming by saying it's figuratively "in the air". But, in this coffee shop, the smell of Viennese dark roast is literally in the air: this contrast of figurative serious mutiny threat and literally coffee both being in the air is funny.