Unlike English, Japan has an abundance of personal pronouns, many of which can tell you something about the speaker.
For “I” there are at least five basic varieties. In Japanese class (outside of Japan) everyone first learns watashi, which is the generic “I”. Except that it’s not used all that much. More popular are the less formal boku and ore in male speech, and atashi in female speech. It’s not good to cross boundaries, either. A man using atashi would get strange looks, just as a woman using ore would. (Although it should be noted that there are some girls in anime, such as Tsukimiya Ayu of Kanon, who use boku, and occasionally popular music sung by female artists is written with boku for “I”.)
The boys in our E-space classes typically use ore, although it’s somewhat of a fad to use watakushi, which is an old form of watashi that is today only used in the most formal situations. Others will use ore-sama—the addition of the super-respectful -sama suffix to the personal pronoun “I” implies a person who is rather self-absorbed and full of himself. I’ve noticed that ore-sama is sometimes used by the villain characters of kids’ action shows (think Power Rangers), so maybe that’s why it catches on with some kids.
“You” is not quite as prolific—three different words that I can think of off the top of my head—but that’s another post.