I've been to some pretty rock-and-roll parties in my time, but I strongly suspect they all pale in comparison to Sir Brooke Boothby's 1783 Gothic pageant. From the Tate's website:
In the summer of 1783, the Derbyshire gentleman Brooke Boothby ... organised a Gothic pageant for the painter Henry Fuseli in the woods behind a house belonging to one Colonel St George, somewhere in England. Involving costume, elaborate stage effects, poetry (penned by the struggling Irish writer Elizabeth Ryves) and an all-singing, all-dancing finale, this midnight entertainment was intended to ‘suprize & amuse the great Wizard painter, who had no suspicion of ye scheme’... Boothby, Fuseli, and the poet Anna Seward all took key roles in the pageant, dressing up, delivering their lines as supplied by Ryves, taking part in the carefully plotted action in different spots in the wood. Their family and friends assumed supporting roles, sporting costumes as fairies, monsters, knights and ladies, singing and dancing, and interacting with the lead players on cue. Curious and amusing as the details of the pageant are, its significance does not lie in the mere fact of its taking place. Private theatricals were immensely popular among the well off in the later eighteenth century, and could take on elaborate forms encompassing the fantastical and medievalising imagery associated with the literary genre of Gothic Romance.
What is striking about this epic revel is the lack of records. There don't seem to be any illustrations (contemporary or otherwise) depicting the proceedings and even its exact location is uncertain. This is unfortunate, but does leave the door open to some wonderful interpretations of the wickedly-intriguing implications. One can imagine all sorts of dramas played out against the backdrop of an ornate, Fuseli-infused Gothic pantomime.
We do have more records of the social exploits of Boothby's contemporary and fellow Gothic aesthete William Thomas Beckford. He constructed the (shoddily built and consequently ill-fated) Gothic edifice that was Fonthill Abbey. Beckford held wild revels there, notably in 1781 only a few years before Boothby's party. Records tell us he employed a dwarf to greet visitors at the main doors (possibly to add to the sense of scale) and his dinners were lit by burning torches held by hooded servants. Guests were treated to ox-roasts and nocturnal turns around the grounds. The building collapsed spectacularly in 1825.
Perhaps the closest thing we have to a record of Boothby's party are Fuseli's subsequent paintings of scenes from A Midsummer Night's Dream. They are utterly fantastical, but perhaps not so very far from the realities of the super-rich at the end of the eighteenth century.