The shocking dashcam footage shows a blue Volkswagen drive out into London Road, Croydon, forcing a cyclist to swerve to avoid being hit.
With the car stuck in a line of traffic and unable to move, the enraged cyclist pulls a massive blade out and launches a frenzied attack.
Brandishing the knife, he kicks the vehicle and slashes at the windows while the driver cowers inside. The victim, a 19-year-old man in an attempt to escape collided with another vehicle, exiting on foot.
After the cyclist moves to the other side of the car and smashes one of the windows, the driver is forced to jump out and run for his life. He was followed by the suspect. The victim later returned to his car after the suspect made-off.
No reported injuries and no arrests have been made after the incident.