Most of us get in the car one way: We lift or squeeze the door handle, and the hinges near the front tire allow the door to open. Then we slide in behind the wheel, and we're on our way.
But why open doors the boring way when you can put those hinges anywhere? Gullwing doors, like the iconic Mercedes-Benz 300 SL of the 1950s, have the hinges at the top, so the doors lift upward and look like the wings of a seagull. There are also "scissor doors" like those of the Lamborghini that have a hinge at the front, but rather than opening out like usual, the door slides upward and out of the way. They were designed to let the driver see behind the Lamborghini Coutach while reversing. That's how horrible the rear visibility was in that car.
But back before World War II, there was a fad in the United States for putting the hinges of the rear doors near the rear tires, so the doors opened "backward." These rear-hinged doors (called "coach doors" in the auto business) had the advantage of making it easier for the passenger to enter and exit the vehicle. No one know why they got the nickname of "suicide doors." There are, of course, many theories.
Some say that if doors hinged at the back weren't latched all the way, they could blow open at speed. Anyone in the back seat who tried to reach for the door handle to close it would go careening out of the car and onto the road. This seems dubious; for one thing, that's more of an accidental death than a suicide.
Others say that gangsters could more easily push enemies out of these doors, which again, is not really a person visiting violence on himself. Another theory says that anyone getting out of the back seat on the street side when parked at the curb could be crushed by an oncoming car hitting the door. It's not a very convincing explanation.
Suicide doors were design features of midcentury Ford, Lincoln and Mercury cars. The Lincoln Continental of the 1960s was quite famous for its center-opening doors. In 2019 and 2020, the Continental was again available in a limited edition with suicide doors. It was a swan song for the Continental, as the nameplate was retired for 2021.
The only holdout for rear-hinged doors as of this writing is Rolls-Royce. It still uses them on its four-door sedans. The idea with these super luxury cars is that a chauffeur would open the rear door from the outside, allowing the rear passengers to exit more easily and elegantly. That doesn't quite explain why the Rolls-Royce Dawn, a two-door convertible, should have doors that open from the rear, but it does.