One who is entering or leaving a vehicle on the street (driver's) side must exercise due care not to interfere with moving traffic.
When accidents result, lawyers argue about contributory negligence. An attempt is sometimes made to show that the driver of the moving vehicle could have averted the accident by slowing down or stopping.
But the fact remains that the law in most jurisdictions puts the burden of avoiding collision on the person entering or leaving a standing vehicle, not on the driver of the moving vehicle.
In the District of Columbia, Section 115 of the Traffic Regulations says, "No person shall open a door of a vehicle on the side where traffic is approaching unless it can be done without interfering with moving traffic or pedestrians and with safety to himself or passengers."
However, in Article X, which deals with pedestrian rights and duties, Section 54 pays that notwithstanding what the rules say about a pedestrian's duties and responsibilities, "every driver of a vehicle shall exercise due care to avoid colliding with any pedestrian upon any roadway and shall give warning by sounding the horn when necessary and shall exercise proper precautions upon observing any child or any confused or incapacitated person upon a roadway."
Unless you want to become involved in a long and costly court battle, it is a good idea to assume that anybody who makes a target of himself is confused and therefore protected by the law.
Being protected by the law sometimes provides a small measure of consolation to those who are struck, but only when they survive.
On the whole, I would say it is better to wait 10 seconds, even in the rain, than to spend 10 days in an intensive care unit. I have done both and can attest that a human being dries faster than he heals.