I had to take one once. I didn't use my blinker and he pulled me over. So he had me walk in a straight line. I didn't do anything wrong as far as I could tell, but he had me do the breathalyzer anyway, then he let me go. I think he was just being a dick; it was a small town and he knew who I was. He ended up getting fired a few years later because he was using an ATV that the police had somehow recovered as his own ATV.
We used to call him Barney Fife.