Luann de Lesseps' Arrest Video Shows Drunken Death Threat to Cop

Luann de Lesseps appeared heavily intoxicated while being put into the back of a police cruiser last year, and even threatened to kill a cop ... according to video showing her arrest.

Footage from inside the squad car Luann was thrown into following her Christmas Eve arrest in Palm Beach has been released ... and you see her tell an officer that she'd kill him if he continued touching her. It appears the cop was loosening her cuffs before buckling her in.

The action begins around the 2 minute mark -- Luann repeatedly says she did nothing wrong, and at one point the officer tells her he's going to hog-tie her if she doesn't stop resisting. Her friends are heard telling her to relax.

As we reported ... Luann was officially charged with a felony count of resisting an officer with violence during her alleged drunken rampage. She's also still facing 2 misdemeanors -- trespassing and disorderly intoxication -- after turning down a plea deal.