Video of the wild incident is, no shocker, going viral ... as it shows the woman telling a plane full of people she didn't "give a f***" about mooning kids and emptying her bladder for all onboard to see.

The woman's trying to make her way to the lavatory but when her path is blocked by a flight attendant, she puts her jacket down on an empty seat, and starts taking off her pants and squats down as if to pee.

For what it's worth, she does say, "Sorry, everybody" ... but then states she's "ready to pee over here" and shocked passengers scream as she starts stripping.

Peepee Patty then stands up and demands to be let into the restroom, as concerned travelers berate her for showing her naked butt in front of kids, sparking a heated argument.

Folks who were there say it all went down on a flight from somewhere in Florida to Philadelphia ... and one passenger is accusing the woman of threatening to kill another person onboard.

It's the second bizarre episode on a Frontier Airlines flight this week ... as we reported, another woman on a flight from Houston to Denver had an epic meltdown with some serious 'Exorcist' vibes.

Holiday travel never fails to entertain!!!