Narrowly averted when this troper was eleven; he and his twelve-year-old not-quite-stepsister (parents dating, not married) nearly Went All The Way but were stopped at third base when Mom and Dad pulled the car into the driveway. Parents broke up shortly thereafter and the opportunity didn't present itself again. Since the incident happened in the summer of 1989 and both parties involved had developed the requisite pubescent reproductive abilities, had the act been allowed to proceed to its conclusion I realized this past summer that I'd be a 31-year-old with a kid about to start college. Waiter, the BrainBleach, please!

You do realize that the chance of actually getting somebody pregnant with an average (IE: fully developed, not 11) size load of semen on a woman who is ovulating at the normal intervals is just under (or was it over?) 30%, right? You would probably just be a very lucky guy if you went all the way.

I'm a gambling man, and I wouldn't lay 3 to 1 against the proposition. I've heard of shotgun weddings where the guy knocked up the girl, but have there ever been shotgun weddings where the woman's son knocked up the guy's daughter?

...Did you find something odd about the idea of an ''elven- and twelve-year-old'' getting to third base, even if they didn't do the deed?

''That'' was the Brain Bleach-ey part of the story for me, not the Not-Blood-Siblings part.

This troper's parents ended up inadvertently becoming this when, after their respective spouses died, Grandpa (my dad's biological father) married Grandma (my mom's biological mother). I shit you not. Squicky or no, it happened five years after his own parents were married and they refused to break up our family just because ''their'' parents were weirdoes.

I'm very sorry, but because there's nothing genetically wrong with that arrangement, I fail to be squicked. In fact, if I were you or your dad, I'd find it hilarious. If I were grandpa, I wouldn't think anything of it, and would give you and dad a weird look if you were squicked out.

Actually, I don't care at all; I just say that to keep the morons from getting squicked. Grandpa's dead now, and dad does indeed find it funny.

This Troper has something similar: Although his parents (obviously) are not related, they share a common cousin because someone's sister married the other's cousin cousin... or something like that.

This troper's family is exactly the same. The only difference is in the times that the respective spouses died and the time difference between weddings. Nobody finds it squicky at all. Some people have found it funny, but that's the extent of reaction.

This troper knows a couple where the whole stepsiblings possibility only came up ''because'' they were dating. The parents only met because their children were dating, and then they started going out. I haven't been keeping up with the local gossip in my hometown since I'm off at college, so I don't know which, if either, of those couples are still going out, but it would be totally weird no matter what.

This Troper once saw a talk show about twins separated at birth. One guy wound up marrying his identical twin's adoptive cousin; they seemed to find it funny rather than gross, though I have to wonder about a woman who would marry someone identical to her cousin.

Clone-fetish?

This troper once had a boss who he was pretty friendly with. She told me one day that she had a relative who married her adoptive brother and had a kid with him. This repulsed her (though, from what else she told me, that was not the worst thing about her).