Most anyone who reads this is likely to know that I'm bisexual, polyamorous, and into SM. One or two people will probably think to themselves, "Oh, so that's why she uses the name WhipArtist", but hey... it's not like I'm hiding anything, and I'll take no responsibility for your not having a firm grasp of the obvious.
On the other hand, if you met me in a poker room, on the street, or in a shop, you probably wouldn't know all of that. You'd certainly notice that I had flaming fuchsia hair, and you'd probably correctly conclude that I'm not a soccer mom or a churchlady, but you wouldn't really figure out the details of my particular flavor of unusual.
When I date people who are in the leather community, I can usually get away with just saying that I'm bi and poly, and that's that. They'll have a pretty good understanding of what I mean, and we'll probably discuss poly details at some point, but I generally won't have to explain what those terms mean and how they work.
If I date someone vanilla, a term I hate but am using with no derogatory intent, it's all different. They can probably grok bisexual pretty easily, though I'll often have to explain some weird details about whether I have to have both at once, which I prefer, and whether I want to have a threesome with them and another woman. Bi is really the least of my worries, though I did once date the only heterosexual man in existence that couldn't cope with it.
Poly is a weird one to explain, since most people who aren't poly don't have a good understanding of what it means, and they don't have a good base from which to talk about things-- there's a huge learning curve around it. This is the one that will most commonly tend to throw a monkeywrench into a relationship, in my experience, and is hardest to understand.
The BDSM thing will either freak people out, or it won't. Sometimes they'll have some sort of curiosity about some aspect of it, and sometimes they'll be perfectly cool but not have any interest in it themselves. Often enough, they'll just find it too disturbing to deal with.
So, when John Vanilla asks me out, I have a problem on my hands. Do I talk to him about this stuff before we go out? Wait until later? How much do I say? How obligated am I to explain details up-front? I'm pretty well-insulated emotionally against someone deciding they just can't deal with any or all of that, but it's still a lot of stuff to absorb all at once.
Even if I find out the person can cope with all of this, there are huge cultural gaps. Pervs are generally used to the idea of negotiating, talking openly about relationship stuff, asking for what they want/need, and all of the stuff that becomes second-nature after you've been around the kinky block a couple of times. People who've only had monogamous, vanilla relationships generally aren't as good at this, and they'll generally have a different base of expectations than I do. It's not that it can't work, but it's like being in a foreign country-- everything is just a little bit more difficult.
I've certainly had good vanilla relationships in the past, but I've also gone out with several people who just seemed like they were from a different planet-- they perceived the world through such different filters than I did that it didn't feel like we had much common ground.
And so that's why I get antsy in situations like this. Even if I'm interested, there's a lot of ground to cover there, and it's generally not so much fun to do it.