This is too funny. What a weird thing to even be thinking about. I mean, the situation you describe clearly happened when you were a little kid, because you "didn't even know that sex existed" at that point.
I have no idea how old you are now, but seriously dude, that kind of shit doesn't really happen after childhood. I suppose it might somewhere, with some freaky, immature, retarded roommate or brother but statistically I'm sure it is highly improbable you will ever encounter such a situation again.
Trust me, you have much, much bigger things to be stressed about. For example, trying to figure out why you're so worried about this situation ever replaying itself.
