Years ago, back when I was young and more stupid than I am now, I decided to drive home after a big night drinking Scotch and water.
I'd had a lot to drink and there's no way I should have been driving. On the way home, I got pulled over for a 'random licence check' and of course they put me on the bag.
Well, I couldn't believe it and the cop couldn't believe it either, but I blew under and was allowed to continue on my way.
Was it faulty testing equipment, or was it that I was drinking still water with my Scotch? I've asked myself that question a few times.