I silently exhale, keeping my face in a polite expression as the man continued talking at me.
At this point, ten minutes into a conversation that I was ready to be done with eight minutes ago, I figured the guy just liked hearing himself talk.
It wasn't like I had been fully interested when I asked my question aloud, but he had seemed to take it as a challenge to become a teacher and teach me everything he knew. 
I fidget, glancing away every now and then, only half paying attention to the voice that was droning on and on and on.
Soon.
I hoped.
Soon he would wind up whatever tangent he'd now found himself in. 
And I would be free to be able to leave without having him follow me around the store continuing to talk.
Soon. 

-Inspiration from watching a customer encounter with another customer.