"Chaos is the only true answer." -Sindri Myr
The Xaositects (kay-OH-si-tects), or Chaosmen, are a faction from Planescape. In essence, these barmies believe that there is no meaning to the Multiverse - not that there is no point, like the Bleak Cabal, but rather that things like order, patterns, etc. are all just flukes in an ever-changing and fundamentally unpredictable multiverse. They preach that Chaos is all that there really is - total blind chance, random luck, pure whimsy. Nothing makes any sense because the Multiverse isn't supposed to make any sense. So, people should just accept that, and embrace Chaos as the only universal truth! Do whatever the hell you want; if you feel like doing it, then you should, because there's no reason not to do so.
...If this is ringing alarm bells in your head, then yes: this is basically a philosophy that worships the idea of Chaotic Stupid, and actually considers this the ideal way to behave. Consequently, "I want to play a Xaositect!" is generally met with the same alarm and hostility as the phrase "I want to play a Kender!"
In 2nd edition, belonging to the Xaositects required a Chaotic character alignment, forbade a character from participating in activities that required long-term organization or discipline, made them freakishly adept at knowing instinctively where lost things were, and let them cast Babble (a reversed version of the Wizard spell Tongues) 1/week for basic membership. Those who attained the next rank (Boss) gained Nondection against Divination spells cast by Lawful sources at level 5, and the ability to shoot off a Confusion spell 1/day that hits anyone within 20 feet and lasts for 2D6 rounds; Lawful characters are -2 to their saving throws against this effect. Big Bosses can have all sorts of weird powers, like Wand of Wonder, a permanent Unseen Servant or Alter Self at random.
In 3rd edition, Xaositect was a prestige class issued in Dragon Magazine #287. It required a Chaotic alignment, BAB +4 and +2s in all saves. It has an appropriately random grab-bag assortment of abilities, including protection from divination by Lawful casters, a vocalizing-nixing ability called Babble, dice-rerolling, resistance to Lawful-aligned spells, immunity to Illusion (Pattern) spells, a Confusion aura, a touch attack that compels random actions in victims, a Chaos Hammer spell-like ability, increased difficulty in hitting, and a permanent Protection from Law effect.
In 3.5th Edition, Xaositects got another prestige class from the Planar Handbook, called the Chaotician. Once again requiring a Chaotic alignment, this warrior-based class lets characters infect others with chaotic impulses that made it harder to defend against attacks by the infector, and eventually get a temporary but undispellable miss chance against all non-area-of-effect attacks on the Chaotician by moving very unpredictably. Similar but not identical to the previous versions of this prestige class, Chaoticians get a resistance to Illusion (Pattern) spells (not immunity), a sound-and-speech scrambling ability called Babble that also nullified sonic damage of any kind, and the ability to call upon Chaos to force one reroll a day, either for the Chaotician using the ability or another creature with no saving throw allowed. As an added bonus for players, LOLRANDOM behaviour is no longer encouraged or required for Xaositects in this edition, just an appreciation (or perhaps even obsession) with the beauty in chaos and a desire to control it.
Xaositects are most known for (aside being a pain in the ass) their use of Scramblespeak, a bizarre verbal cipher in which random words are jumbled out of order in various sentences at random, which is likely decipherable only to other Xaositects.