Well, like many things, it started in Finland. In 1996, the first Air Guitar World Championship was held in Oulu, Finland. But this is America! I can hear you shouting, over the sounds of racking your shotguns. Well, America decided to get in on this party with something that, let's be fair, truly is an American pastime (who invented rock 'n' roll, after all?), back in 2003.
At first, it was small, with 2 regional competitions feeding into the national finals - and the national champ going on to Finland. But it grew swiftly, particularly after the publication of Bjorn Turoque's seminal text, To Air is Human, and its associated movie, Air Guitar Nation.
In 2013, there was been a big change! Instead of the national organization, US Air Guitar, traveling to upwards of a dozen cities each year to put on a regional competition there, they are now having 4 semi-finals in different geographical regions, and individual air guitar aficionados in their own cities can put on a qualifying round that will feed into one of those semi-finals. Boston has one such qualifier (This year, it's on May 24th at TT the Bear's! For more info, see this blogpost).
- Technical Merit - are you more or less doing the right hand movements to match up with the song? It doesn't have to be perfectly precise (although it's fantastic when you are!) - let's be fair, the judges can't always even see what strings you are invisibly touching. But they can tell if you're strumming when the guitar in the song is not playing, for instance.
- Stage Presence - do you have it? Are you using the whole stage? Are you getting your audience engaged? (note: you do not need to actually get engaged to an audience member, although presumably that wouldn't hurt)
- Airness - this one's kind of hard to explain, but really it's how well do you turn this into an art form? People air guitar in their bedrooms and idly at the bus stop and that is not a performance. This is. Does it look like one? Are people screaming their heads off for you? Do people say "Whoa." afterwards? That's airness.
Also, you get to pick an awesome air name. And at the end, everyone - participants, judges, spectators - is invited up onstage to air guitar together to Free Bird.