Coffee beans are big.

Not from the Hitchhikers' Guide to the Galaxy:
"A coffee bean," it says, "is big. Really big. You just won't believe how vastly hugely mindbogglingly big it is. I mean you may think it's a long way down the road to the chemist, but that's just peanuts to a coffee bean, LISTEN!" and so on...

Okay, we all know a coffee bean is rather small; small enough to be quite challenging to manage to choke on one. Since choking on food is one talent humans have monopolized on planet earth, we had to find another way to make the bean dangerous, a worthy opponent. Thus, we balance hot coffee in flimsy Styrofoam cups between our legs while driving 5 speed manuals with temperamental clutches through Boston rush hour traffic while texting how terrible other drivers are.

But still, coffee beans are quite large in comparison to those things that make up most of the universe:

http://learn.genetics.utah.edu/content/begin/cells/scale/