What i have found in my personal experience, is that a LOT of people don't even know what BDSM is. I'm very open about it to people, and i freely discuss it with anyone if they wish to hear.
I usually havre to go back to S&M to draw any kind of recognition to the idea of it. It seems to be the most commonly acquainted aspect of it. From their i will expound on how it is more than just sadism and masochism. I try not to go too far into the dynamics of it because i know i will lose people. I try not to explain things in the context of emotion because again, they will not likely understand.

I show people my scars sometimes and they ask me "didn't that hurt?" (rhetorically, i assume). It seems to me that most people that don't know or don't understand it, want to know WHY. Why do the people involved in this sub culture have these desires and how are we ble to put ourselves in the position to have them fulfilled. Aren't ewe afriad of getting irepably damaged? Aren't we afraid of irrepably damaged someone? Are we a control freak? Why do you want someone to order you around? It's mostly just an inability of being able to relate that I think throws people off. My best response is to compare it to the things that they enjoy doing in life that all have their own little risks and specified interests. for instance.: I don't enjoy dirt bike racing and i don't understand why someone would put themselves in the position to become financially, legally, and physically in danger for that rush. But people do it and it makes them happy.