It's difficult to say, really, and depends on the person. For Slaanesh him/her/itself, every form of emotion is considered excess because it feeds him/her/it. Everything from the insane and deprived shit its followers get up to, or a tender moment being shared such as >>52710800
. Every emotion of love, or hate, or pain, or pleasure, all of it feeds Slaanesh in some way; EVERYTHING is pleasing to Slaanesh.
Each cultist is, I'm sure, a little different in what they love to indulge. One who is obsessed with all kinds of kinky and disgusting sex, for example, would find slow and passionate sex to be a new (and excessive) experience. I think it's less the amount of excess itself, and more the type. If you were constantly high and shit like cocaine, marijuana would be a new type of pleasure to enjoy, even though it's less stimulating to your senses.