Think about this one.
If you haven't figured it out, I run with a group of people who like to push the limits of what the law 'allows' supposedly free and sovereign citizens to do. So, I end up interfacing with Cops quite a lot. OC isn't the only thing they like to cross the line about.
Often, cops like to approach you and take you aside 'to talk.' They have a list of good reasons. "Don't want to embarrass you in front of your friends," "It's too loud," or just flat out "Lets go where we can talk privately."
Herp a derp! The Officer wasn't doing it for you. He just created a reasonable Expectation of Privacy and you let it happen.
They spend a lot of time thinking up ways to do this. They have lawyers paid for with your money figuring out just the right words to use. They teach it in the academy. Crossing the line as often as possible while creating a fall back of Qualified Immunity is what they're all about. If they pull you aside like that, and you agree:
1) You've just agreed to being detained, forget USC42 1983
2) You've just made it illegal to record the conversation, forget any evidence of the threats they just made on your family's life, etc...
Subtle little stuff like that is how they get away with violating The Constitution. They live for it. Think about that. They and their lawyers get paid with your money to think up ways to violate The Constitution and get away with it.
They're good at it. They craft it to look benign, or as if they're doing you a favor. They're not 'just doing their job' when their job is to strip you of your Rights and Freedoms in any dirty little way they can.
How do you know if some guy you don't really know who wants to 'speak privately' is a cop or not? Will you be able to prove it later when the evidence isn't admissible because of that handy Reasonable Expectation of Privacy? I speak from experience, having had Officers threaten my family and myself. No reason you have to lose your evidence against them, too.
