Anybody who's heard any Little Johnny jokes knows well enough to expect something vulgar. Here are a couple (sorry if they've appeared in other joke threads).

Little Johnny's in school one day, and the teacher says, "OK, class, today we're going to learn a new word. The word is 'URINATE.' Now, who can tell us a story that has 'URINATE' in it?"

Little Johnny is the only kid with a hand in the air. Knowing his propensity to be nasty, the teacher says, "Surely more of you are familiar with that word." Still no more hands are in the air, so she says, "All right, Johnny, tell us your story."

Grinning from ear to ear, Little Johnny chimes right in, "Me and my family went to the beach last weekend. This drop-dead gorgeous babe walked by, and right in front of my mom, my dad says to her, 'Yer an 8. If you had bigger tits, you'd be a 10.'"

The next day after school, Little Johnny is sitting on a park bench with a bag full of candy bars, happily stuffing his face. There's an old man sitting next to him who can't help notice. Finally, the old man says, "Son, you need to slow down with the candy. It's not good for you. If you keep on eating as much as that, you'll get fat, get pimples, and it'll eventually kill you."

Little Johnny glares at him and says, "My grandpa lived to be 110 years old."

The old man asks, "So, did HE eat that much candy?"

Little Johnny says, "No. He just knew when to mind his own f--kin' business."