Maria Shriver -- Sweet Street Justice!

The rebellious First Lady of California was walking out of Peet's Coffee in Santa Monica when a vigilant parking enforcement officer noticed her meter had expired. The officer pulled out his rusty, trusty "auto-cite" device to ticket the vehicle, when suddenly one of Maria's security dudes ran up to him, flashed something at the officer and did some fast talking.

In the end, the officer backed off without writing a ticket. Maria then got in her SUV, took off her glasses and began eating her muffin as the expired meter continued blinking.

Oh, and there's this .... she drove off without securing her seat belt.

A Santa Monica police official tells TMZ writing a parking ticket is "discretionary." He also said if Maria was on official business she'd be exempt from parking laws, provided she had a placard on the dash. We saw no placard and -- last we checked -- eating a muffin is not official business.

UPDATE: A Santa Monica police official now tells TMZ the parking enforcement officer was about to write the ticket when a man walked up to the officer and said he was a member of the CHP Dignitary Protection Unit. The CHP guy then said he understood the officer had a job to do but the dignitary would be gone in less than 5 minutes. At that point the parking enforcement officer backed off, but issued a warning.

As for Maria then getting in the SUV, eating a muffin and driving off without her seat belt, the parking official says his officer didn't see that.

We contacted the CHP -- they have no comment on the situation.