Flying Brothel

And also a warship. "Murderbarge", Hades Class Heavy Cruiser, carrying the Mark of Slaanesh.
Youngest Chaos God, Slaanesh domains over pleasure and excess, so it's no wonder people see him/her/it as the "God of Sex, Drugs and Rock'n'Roll". In Battlefleet Gothic Armada, ships aligned with Slaanesh increase the chance of enemy captains fleeing the fight out of insubordinations (Especially dangerous vs. Orks, totally useless vs. Imperial ships with Navy favor, but it's passive ability) and can shut down enemy ship's orders and special abilities for some time (Shutting off Eldar Pulsars for example).
That part with the Eldar seems correct: since Slaanesh was born by Eldar and had their pantheon as well as a lot of them for a snack, pointy-eared flakkers fear "Her Who Thirsts" (as they call it) more than ANYTHING. Considering that this is Warhammer 40k universe (And considering what kind of people Dark Eldar are), this speaks volumes.