I wouldn't say I'm vanilla haha. I've done almost everything you can think of when it comes to sex (with women), but I've never been into hardcore BDSM. I've never found it appealing.
Hard to explain. When it stops being just powerplay, and starts being too physical. While I have high pain tolerance, I don't find it pleasant in a sexual way to inflict or experience physical pain like you (unfortunately haha).
I've noticed that people always equate the term "vanilla" with "boring", and therefore react adversely to this label. In my experience, the term "vanilla" really only refers to non sadomasochistic. It's just another flavour. Not my preference, but variety is the spice of life.