What it says on the tin. Canon-AU for Season 3 (obvs the finale hasn't aired yet so no real confirmation that it's canon-compliant)

Stiles would say his relationship with Derek is about fifteen percent empty threats, thirty percent sass, ten percent avoiding violence together, and five percent eyebrows. If anyone asked, he would say the remaining forty percent is mutual orgasms. It’s a good thing no one ever asks.

Pornstars Derek and Stiles work for the same company. Derek only shoots with werewolves and Stiles only shoots with humans. That's not going to change after they meet. It's really not. (It might.)