Aubrey O'Day -- Hit-and-Run Driver Threatens Her with Heavy Metal

Aubrey O'Day had a rough Cinco de Mayo -- not only did her BMW get smacked up in a hit-and-run, but she got threatened by the alleged culprit.

Law enforcement sources tell TMZ ... O'Day was a passenger in her own car on May 5 (fellow Danity Kaner Shannon Bex was driving) when a giant SUV hit her whip as it sat at a red light.

We're told the black Buick Enclave rode halfway up her hood before the driver gunned it and beat a hasty retreat. We're told the impact was bad enough to cause $10K in damages.

O'Day and Bex went to a hair salon the next day and spotted the phantom Enclave. They took a few pics of the car for evidence, when the driver came out and confronted them.

We're told the Enclave driver allegedly went inside the salon, brandishing a heavy metal object and then asked the women, "Do we have a problem here, 'cause we can take care of it now."