Actor Jensen reads script. Sees BDSM upcoming. Gets convinced/coerced to do it outside of filming.
In the story, I remember that Jensen read ahead in the script and discovered that he was going to have to be introduced to BDSM in it. It was something like Sam being soulless again, Cas going evil, or Crowley kidnapping him. I can't remember. The point was that for at least one ep, maybe several or the season, Jensen was going to have to wear a collar and that sort of thing. What I remember most was that someone convinced Jensen to prepare for the role by exploring BDSM. I kind of remember someone or something (like the network, producers, director, etc) convincing him that he should do a method acting thing where he committed to it. Even outside and that it would be a good publicity stunt or promoting material if he was caught and photographed like that (like with a collar) while out doing his thing. Doing it for the fans... There may have been a humiliation aspect to it, but I can't be sure.
That's all I can remember.