Seriously, dudes -- this is a lot like a pedestrian going for a demo flight, and after which they said "this isn't rocket science, anyone can do that".
I'd respectfully say that ya don't know what ya don't know; just as the demo flight guy hasn't even scratched the surface of all the knowledge and decisionmaking and judgment required to actually be a "pilot", I'd argue that untrained guys don't know what you don't know when it comes to what is required when flying safe formation. Just like it isn't too terribly difficult to herd a GA airplane around in flight, it isn't too difficult to get two airplanes close together when flying around at up to 30 whole degrees of bank and manage to not hit each other. It is handling the "what ifs" that make someone a formation pilot rather than just a guy who is flying close to another airplane.
If it were really that simple, you wouldn't have/need organizations like FAST or FFI to teach and certify it. @
ppragman's rules are important ones, but they are so overly broad that they miss the actual skill in how to accomplish each one of them. There is so much depth to each of those (and there are more "rules" than that, FWIW) that it is just as unrealistic as saying to be a 121 pilot all you have to do is "not crash" or in order to make it through military pilot training all you have to do is "not suck". The devil, as they say, is in the details.
In all honesty, formation flying is not that tough to learn or perform at a basic level. I teach much more complicated formation aerobatics and maneuvering in a supersonic jet to hundreds of 20-somethings per year. I'm confident that any of you on this board could learn to be very safe wingmen (not flight leads) in GA aircraft with a handful of flights and a couple hours of academics. It would take more experience and training to become a formation leader after being a wingman. The cornerstone to doing that safely, though, is learning ALL of the important parts in a controlled environment with defined roles from instructors who know what they are doing. To do otherwise, IMHO, is a serious risk to your safety and whomever you are flying with (because, remember, when there is a midair in a formation -- unlike when a solo pilot does something stupid which just results in him getting killed -- there are at least two pilots whose lives are in danger).