Dattebayo!

[Ladywriter]

It was starting to drive me a little crazy, Naruto and his damn dattebayo at the end of every other sentance. I've listeded to a lot of J diolouge and that was a new one to me. The english version of Naruto has him saying "belive it!" all the time so I was like :wtf:
Anyway I went looking to figure it out. -_-; Pretty much it's just another way to end a sentance to emphasise what the speaker is saying. It's makes the sentance more agressive. The speaker is making sure they're being heard. Their strong will is coming through.
Naruto uses this expression a lot because he has always been starved for attention and acknowledgement. It also expresses how strongly he feels about what he's saying. Naruto dont take back his words. That's his way of the ninja :p

[Eppy]

that stuff is common a lot like -nyu and the such after every sentance

[Godgrave]

Similar to how they'd use Yorokonde (spl?) aka Chobits. But Naruto says a lot of Dattebayo in some episodes.

His way of the ninja - Become Hokage, not going back on his words or promise, eat Ramen ^_^.

[EVA-01]

The only reason I think they put it in is to fill in the extra voice movement for him. "Believe it!" gets old, quick. All of these Naruto n00bs at my school keep on saying that stupid little phrase. =_=;