Should I be insulted?
At the beginning, JEANNIE accusses WARREN of being cheap. Throughout the movie, we see him using public payphones a couple of times, and everytime the call ends, he searches for change in that part (I don't know what it's called) where you get your money back if the other person doesn't pick up. Because of the kind of movie this is (and the kind of director Alexander Payne is), I'm sure that's included on purpose.
I do that all the time. Not because I'm desperate to get my money back. I do it mostly as a reflex, in case the machine makes a mistake and drops the money.