Dirty Joke Number One
Sex jokes are a very significant thing for small children, I feel, because they're a sort of mystical portal into a mysterious "adult" world. And I can remember the first one I heard, with a group of friends (as told by: Luke. Hi there, even though you're definitely not reading this; I know you're not dead, though, as I'm friends on facebook with you and also your mom and sister). I must've been seven or eight at the time, and it's worth noting that I really had no idea about sex at the time: sure, I'd asked my parents where babies came from and gotten the clinical answer, but, uh...I mean, I guess I got that babies emerged from women, but seriously "the man puts his penis in the woman's vagina and sperm comes out." Great, but I was still totally in the dark about what exactly a "vagina" or "sperm" was. Jeez!
Anyway, this is a pretty darn basic joke. You can find it all over the internet. Here it is: there's a classroom. A boy walks in late and, when questioned as to his whereabouts, replies "I was on top of Blueberry Hill." Repeat this with more boys as often as desired. Finally, a girl comes in and says "Hi! I'm Blueberry Hill!" DO YOU GET IT? I sure as hell didn't, I'll tell you that that much; I couldn't speak for my friends, but we all laughed knowingly, because obviously it was extremely vital that we not be seen as lacking the numinous information that was obviously implicit in this incantation.
I'll tell you, though, I remember very vividly the visual image I had in my head upon hearing this, and that was of poor Blueberry with all these boys successively standing on her shoulders, like a totem pole. I suppose that could potentially develop into an extremely strange fetish, but all it gave me was this anecdote. I guess that's a pretty good joke, when you think about it.
Father Spermatozoid talks to his son.
"Son, one day you will noticed you are in a tunel, and there will be plenty of your friends there all heading into a single direction... try out-race them as hard you can! If you manage to do it you will enter an large chember and there you see a large ball... introduce yourself politely and then quickly try squiz yourself inside"
"Fine father, I shall take this wisdom"
So some time passed, the Spermatozoid is having a lovley day and... BANG! He notices there is plenty of his friends passing him all heading into a single direction!
The little Spermatozoid goes "Oh, crap!" and with all his might he speed up to be infront of them. He manages to leave compation waaaay behind, and take a deep breath in relief, but then... He stops! To his confusion THERE ARE TWO BALLS!
"Um, hi..." - he says akwardly - "I'm Spermatozoid..."
The balls smile and reply
"Yo! We're the tonsils!"
Perhaps sounds better when I tell it in Polish, but anyway - One of first sex jokes I remember and I recall when I told it to a group of friends, one girl went "HA-HA! He mistaken direction" (which is an even better punchline)