Bruce Lee did dragon flags often, but they were popularized by Rocky when he was training to beat the hell out of Ivan Drago in Rocky IV. They're exceedingly tough to do, especially if you've never done them before. They're also pretty much the most impressive looking movement you can do in a gym.
Even though they're tough to master, this relatively easy progression takes you from reverse crunches to true dragon flags in no time.
For years, I've been watching zombies, training zombies. They wander aimlessly from station to station, doing exercises haphazardly with really no rhyme or reason except that, "this one kinda' feels like it's doing something." Once in awhile, they'll grasp on to a particular program but they'll end up beating it into the ground, doing it for months and months until they've long since milked any effectiveness from it.