At 300 fps it's roughly 0.75psi dynamic pressure, so on a 5 inch thick * 80 inch (edge-on) door, about 300 pounds of force. Seems a bit high for a person, but the passenger can get some good footing to brace that motion. At 200 fps it's down to only 130 pounds of force.
How glorious - 1 foot per second ~ 1 kph and 1 kph is about 0.54 knts.
Not only keep your seatbelt on but also stow all items in preparation for landing.
Comparisons to car doors are a bit off as most people in cars would be using only their arms and not have a good position to apply much force and would be applying that force at the door handle, which is close to the hinge, decreasing the leverage they do have. There is also the non-linearity to the typical car door - the force increases as the door opening widens, where in this case the force is about the same once the door completely enters the airstream. It might even ease up a bit on the plane if the leading edge of the door enters first and is deflected outward by the oncoming wind.
The easy means to prevent this from happening in flight is keep the cabin pressure on a little bit until the plane exits the runway. Set the cabin altitude to 2-5000 feet below the runway altitude - that should keep the door shut. Bad news - that would add more ear drum distress to everyone else because of this twit.
This should be a reminder that if anyone is out of their seat when they should not be - everyone nearby should be out of their seat to stop them.