I didn't say be belligerent. I just said don't tell them anything. You can do that very politely. "I'm just sitting here in my car deciding if I want a latte' or a capuccino, officer."
Yes, but I would NEVER ask a cop if I were under arrest or if I were being detained illegally. Diplomacy works best with cops because you never know when you are dealing with someone drunk on power. You always want to act as if you are on their side and respect their authority, even if the cop you are dealing with is a stupid jerk.