Nah, no point. Underlying your approach is the desire to make these people feel bad. A) you can't do it, they have no sense of guilt, and B) how would that make you feel any better?
No. Underlying my approach is my desire to defend myself from people's idiocy.
Here's an example in which I would've benefited tremendously from carrying around a discreet voice recorder.
I used to work in a restaurant as a waiter, and the restaurant would get quite dead in the late afternoon, after the lunch rush and before the dinner rush. Usually there would be two people scheduled to fill this lull, one would work until 4:00pm and the other until 5:00pm.
On this day, I was scheduled for 5:00pm. At 3:00, after there had been no customers for an hour or so, I went to the manager and told him this, and suggested that he cut someone. He told me since it was so dead, I could leave. I shrugged, gathered my things and left.
This ended up being a problem, because I left at 3:00pm, and the 4:00pm person, predictably, left at 4:00pm, leaving no wait-staff on from 4:00pm to 5:00pm.
The next day, he approached me livid, because I had lied to him and told him that I was only scheduled for the 4:00pm slot, and that I had purposefully screwed him over, and several invectives. When I tried telling him that he was wrong, he only grew angrier.
So, this is the main point of carrying a voice recorder. People do not accurately remember what they say, or what you say, and take extreme liberties with this later on down the road based off of current circumstances and their emotions (which these people allow total free reign).
how would that make you feel any better?
Now, it just so happens that I do take pleasure from throwing people's idiocy back in their face in a way that they can see it, if they're bothering me. So that answers this question.