Except that a Vermont judge recently ruled that password(s) contained in one's head are protected under the 5th Amendment to the United States Constitution. just like any other information in your head. It was discussed right here on Slashdot.

As for threatening law enforcement officers: say nothing, know your rights, and keep your cool. The law enforcement officer is NOT your friend and you shouldn't speak to them or answer their questions. You have a right to remain silent and you should use it. BTW every attorney that I have ever heard opine on the subject has said that it is better to say nothing than to answer some of the questions but not others. Don't let them scare you into giving up your rights with their Gestapo crap. Remember, if they are questioning you, especially if they are threatening, then there is NO way that you are NOT going to be held (i.e. arrested) for a while anyway until the matter either goes before a judge or they have to let you go (48 hours max w/out cause before any attorney can force them to let you out), so don't be dumb and tip your hand right at the start. Also, remember that if you ever get your equipment back then you can never use it or those passwords again (who knows what bugs they may have planted before releasing it back to you). You basically have to wipe and start over on new hardware.

Disclaimer: IANAL so if you find yourself in a situation like the one above find yourself one that you can trust and let them do the talking, but remember that the police are NOT your friends.