There’s a continuum of crazy in the world of conspiracy theories. On one end are the at least somewhat plausible ideas like that Oswald didn’t act alone in the JFK assassination. On the other end are the downright schizophrenically crazed theories, say that the world is actually run by evil reptilian aliens in disguise.
I’d put the chemtrail folks down toward that crazier end. They are of the opinion that the trails left by jet aircraft are in fact government chemicals of unknown but certainly nefarious purpose.
Roughly it’s akin to the phenomenon of breathing out on a cold day and the vapor-saturated air condenses into droplets when it cools. The mechanism is entirely different in this case, but the general concept is not so far removed – the air was able to support a level of water vapor, and now it can’t. Bam, visible water.
In the case of this F-22 and the other circumstances in which it’s observed (it’s not a new phenomenon at all) the thing that’s changing is pressure. As the shock wave passes the pressure drops, the water condenses. Once the shock wave has passed by, the droplets return to vapor almost instantly. More or less anything with a big shock wave can do this, not just aircraft. Here’s the Castle Bravo thermonuclear test, with the upper portion of the mushroom cloud formed by the same effect:
Yet another variant of the effect was used in early particle physics. Subatomic particles move through supersaturated vapor in air and leave cloud tracks behind them. That technology is obsolete today, but it was instrumental in many early discoveries.
But even if it were only good for snazzy photos of airplanes, it would still be interesting.