The one backing out, because you should realize someone is opening a door.
Speaking from experience if a person opens their care door into a lane of traffic, they are responsible if it gets hit. If you legally go around a car that is double parked and the occupant opens their door and you hit it, they are responsible. Don't move. Call the police.
driver of parked vehicle
The person who opens the door.
YOU, as the driver, are responsible for the actions or failings of your passengers. Ethically and legally you are required to notify the damaged vehicle owner that your vehicle caused the damage and then either turn the claim over to your insurance company - pay for it yourself and have your friend reimburse you for their carelessness.
the person who opened the door
The insurance company of the car whose door was opened will pay for it.
The driver/passenger opening the door is at fault. Look it up under the traffic laws in your state.
Using the handle which opens the doors. Instead of pulling it as you do to open, you push it in until it clicks.
It opens by pulling the handle at left in the drivers foot space.
Impossible to answer without a detailed description of all markings.
No. If he entered your apartment legally, he may exit. Otherwise, you will have a maintenance guy living with you.
It completely depends on your state laws. In California it would not be, but in Utah it would.