Slaaneshmas is a holiday created by Lucius the Eternal as an effort to provide Slaanesh with more variety of emotions. Instead of torturing victims, for one day Slaaneshi cultists treat others nicely. Lucius and Ahriman used a broadcast relay to hijack all HV networks in the Imperium to broadcast their own Slaaneshmas special to coincide with Sanguinala, styled after late-night talk shows. Guest appearances included Kaldor Draigo, Typhus, Sly Marbo, Miriael Sabathiel, and Fabius Bile. Toward the end of the program, Lucius and Ahriman offered the Imperium an annual one-day ceasefire so that Chaos and Imperial forces alike can be united by their common Humanity (and more importantly, their shared xenophobia) and kill aliens together.
A competing holiday is Great Horned Rat Day, devoted to the eponymous Great Horned Rat, who feasts on the "nonexistent" corpse of Slaanesh.