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M*W: If you get pulled over for something, you are not under oath. It's only under oath when you should speak the truth.
That's not entirely true. If you are found to be purposefully deciving them about things you are required to tell them, like your name, you can be detained and possibly arrested depending on the state.
Most states if you are driving you have to have a valid license and proof of insurance. Non drivers usually can be required to identify themselves verbally.
Even if you aren't driving, if you are intoxicated in any way, don't be a jerk. A cop can arrest you on a PI charge strickly on his personal assesment of your behavior. Even if you beat it later, is being an ass worth a trip to the station?