Normally you have to do it in second gear. Getting the engine to pop off in first or reverse is tricky...takes lots and lots of practice and a low compression engine. Having the engine over the drive wheels helps too. It just might be that a VW beetle is the only car that it can be done with.
BTW, people die from going in reverse with one foot out the door. If the car is small enough, the front wheel will run over your foot when your leg is fully extended...it pulls you out of the car and under the wheel. At least on a front wheel drive it does.
I was thinking about this, and I think I actually did manage to push-start my car a couple of times, by parking uphill. It was a 1972 Olds Vista Cruiser with automatic transmission, so it certainly wasn’t easy to push-start. I didn’t think you could push-start an automatic, but my wife swears we did it, and I remember doing it.