In the early stages of my formative youth, I was merrily getting dressed for PE in my own little corner of the boys' changing room whereupon my bully for the year decided to break the wide circle of people avoiding me to ask me if I had ever had a boner. Not knowing what this was, I asked him - well - what it was.
I hasten to point out that I genuinely didn't know what an erection was. I'd known the basic mechanics of sex since the age of 2, but I'd imagined it to be something like sliding a flaccid penis into the anus. You know, if I'd wanted to imagine it at all. I'd missed the video in year 5, and now I was in year 7 I still didn't know, because we did the bit of biology later in the year.
"That's when your cock gets hard," gloated my bully.
"Oh, yes," I answered honestly, "I get that when I get a feeling of power."
My bully looked as if Christmas had come early.
I have this unsettling ability to be genuine and honest about things, even if they're uncomfortable things - and in my innocence gathered during my 11 years of age, I felt confident about answering this honestly, because I had no idea it had anything to do with sex. Yet I did have erections when I got a feeling of power. That is what happened.
Before you start accusing me of being a seriously weird kid... well, I was a seriously weird kid, but it's still an odd situation, because sexually I've always been a fan of the partners being equal. I'm not into BD/SM at all (although during light roleplay I usually assume the dominant rôle, but that's 'cuz I'm a good actor) and although I do enjoy a certain degree of power, there's a difference between being the owner of an IRC chatroom and a Dark Overlord who abuses and occasionally eats his servants.
Which was my bedtime fantasy. You know, despite me being a pacifist vegetarian. It probably wasn't even a sexual thrill that gave me an erection, it was something about the feeling of either control, or revenge (during one dream I was a monstrous plant who ate the older boys who threatened me while I was skating on a dirt mound - most of the dreams involved eating people, I know not why, maybe I was genunely twisted). It was an odd kind of power, almost evil, although I've always been allied with the forces of good in real life, that I dreamed about, and this gave me an erection.
Of course, when I found out what it was, I quickly retracted my statement to my bully, but he'd spread it around the school. Fortunately, by this time he'd also spread it around that I was gay (because that's a bad thing when you're in year 7, apparently), so that made people shun me, rather than anything else.
And from that moment on my bedtime fantasies - under my control this time - were about being encased in a special machine to have sex for years on end... but that's a different thing entirely, and a very different erection. Hey, what can I say? I was a seriously weird kid!