At the start of 1974 Robert Opel was a freelance photographer for the gay newspaper The Advocate (now a leading national magazine). When he showed up at the Academy Awards he used these credentials, and a great deal of exaggeration to make himself appear a more significant journalist than he actually was.

Once Opel was in, he knew that his incongruous appearance could have potentially raised red flags before the stunt was attempted.  He made his way backstage and hid inside an enormous piece of scenery.

And then boom!  Out he goes.  The best part is how well David Niven handled the whole thing.