A few general traffic laws apply:

1: The UFO is not a legally registered road vehicle and they must yield to all traffic.

2: If you see a hazardous situation, like the UFO not clearly following traffic laws giving you space, you must do your part to avoid injury by avoiding a collision.

So after you do brake for the UFO, or swerve and honk, you may go to the police and inform them of the aliens’ traffic violation. They may then get a fine.

If you say “fuck it Im in the right” and crash into them, you are both breaking the law, but you are in bigger trouble for willfully endangering life and property. You get prison, the aliens get a fine.