Reese Witherspoon wasn't kidding when she told GMA she was "saying all kinds of crazy things" ... and TMZ has obtained the entire, unbelievably entertaining dash cam video.
The footage, obtained from law enforcement sources, shows the officer arresting Reese's husband Jim Toth for DUI in the early morning hours of April 19.
Reese -- who since admitted she was hammered at the time -- decided to butt in during the arrest ... and the officer obviously wasn't having it and cartoonishly enforced the law with a vengeance.
In fact, the cop warned Reese several times to sit down and be quiet so he could focus on Jim -- Witherspoon didn't exactly comply.
Instead, Reese got in the officer's face ... and annoyed him to the point that he arrested her for disorderly conduct.