Cardi B Concert Fight Ends With Hot Dog Left on Hood of Bystander's Car, on Video

Cardi B was NOT the drama on the opening night of her new tour ... but her fans were!

A parking lot brawl broke out after the show, which ended with an innocent bystander's car getting a hot dog splattered on it.

You gotta see this video ... it's completely unclear why these women were fighting, but it's also totally irrelevant. What's important is, in the middle of the tussle, someone drops a fully-loaded hot dog on the hood of a pristine white car.

The driver and passenger of the vehicle watched the scene unfold, got it all on video, and blessed us with some hilarious commentary.

"Oh f***! I told you to move your car," one of them says with a laugh. "Oh my God, you got a f***ing hot dog on your car!"

Then, laughing so hard he can hardly breathe, he goes, "They didn't even take the hot dog!"

You have to hear their cackle as they drive off with their new hood ornament. In the video, you can see spectators pointing and laughing at them, too, as they pull out of the parking space.

The Riverside County Sheriff's Dept. tells TMZ ... at about 10:30 PM Wednesday, deputies responded to a report of battery in the lot. Paramedics treated one person at the scene for a minor injury ... and deputies say one person was arrested and booked for battery.