Think "air guitar" but with more dry-humping.
OK. Are you familiar with "air guitar?" It's the awesome intersection of hard rock, hard rock appreciation and wild exuberance. In fact, if you're not familiar with "air guitar" you should consider getting out more, for realsie.
But as awesomely outrageous as improv-ing sweet rock moves is, it's not quite as awesomely outrageous as the endgame of any sweet rock concert: the sex. The "unholy trinity" of Sex, Drugs and Rock 'n Roll, though cyclical, always seems to wind up back in bed (or a tour bus lav, depending). That's why some enterprising lads (and probably a grand total of three ladies) have decided to skip the mimed Fender Stratocaster (I've always been a fan of "slappin' da [imaginary] bass") and move right to the imaginary sex moves*. According to The Week, the new trend sweeping the nation is "Air Sex." (Note: it has little to nothing to do with the Mile High Club.)
"Air Sex" involves no actual nudity (or even actual, physical contact, but floors and mic stands are known to get dry-humped). It's just a bunch of rude dudes getting lewd while getting in a mood to get screwed. Translation, a bunch of fun-loving funsters pretend to make sweet, sweet lust to imaginary people and get judged for it (think critiqued, not castigated). Like many sex-related craziness, "Air Sex" is said to come to us from the Japanese.
Just like freestyle walking became "Parkour" when someone videotaped it, "Air Sex" (doing the motions of sex acts to not existent partners) has been around for years, if not millennia. I'm just glad that someone attached a name to it so that parents can be afraid of it like they are "sexting" or the swine flu.
From personal experience, "Air Sex" can either enchant (i.e. "bring all the boys to the yard") or incite the worst in people. A friend, covered in rib sauce and partway intoxicated, once acted out a serious of sex-stuff that progressively became more debauched to the point that a single, unarmed man attempted to do bodily harm to four grown (but highly immature) men to put an end to the show. And that's all you really need to know about "Air Sex," sometimes it awakens a long-dormant part of your sexuality and sometimes it so incense seemingly rational people to the degree that they commit acts of public violence. See for yourself on YouTube (sort of Not Safe For Work).
*Note: While pantomiming drug use is hilarious, it's sometimes tough to tell the difference between pretending to hit a bong and providing fellatio.