It's naruto from the anime Naruto's catch phrase.
He ends every f ing single sentence he speaks with that word.

Dattebayo is a word that Naruto Uzumaki adds to the end of his sentences. He uses it to make his way of speaking unique. It adds emphasis to whatever he says

Dattebayo actually has an unclear translation to things like:
"This is what I'm saying"
"Y'know what I'm saying"
"I mean it!"
"I'm saying this!"

Dattebayo, however does not mean believe it. Believe it was something that Viz media came up with to match the dubbing.

The catch-phrase of Naruto. The main character of the anime/manga seires 'Naruto'.

In the English version Dattebayo was translated to "Beleive it!" Much to the dismay of hardcore Naruto fans.

A group of people who fansub anime.

Known for two things:

1. Loving Naruto (which is the new Dragonball Z for idiots who love shitty action shows).

2. Being gigantic, unfunny pricks.

You think that powerfully built He-men who devote huge time to telling Americans what cartoon characters are saying, would have the social graces of a Victorian era countess and the speed and grace of a winged jungle cat but, it turns out these guys are a healthy mix of scrawny pigeon chested dweebs and, Crisco coated lumps of fat and beard.

They also like to "troll" by wasting everyone's' time with gag subs and limp wristed, obvious fake news. Apparently when you translate crappy cartoons from your mother's basement, it affords you a bit of free time to display your lack of any real humor.

They are also ballsy enough to write YHBT at the bottom, so as to identify their laddish crap before you even fall for it.

They enjoy posting the constantly -banned for sake of enjoyment- I.P.s on their website because that makes them edgy and hardcore. They're also hoping people who made them cry will be "teh haxxored".

Even though the hacking skills of the 13-17 year old narutard fanbase they've managed to sop up are all 150lvl Blackhats, with +5 to all hacking skill checks and saving throws,

The results have been disappointing to say the least.

Dattebayo does have a meaning. It means in Japanese "You know". In English It was changed to "Believe It" to match Naruto's lip movements. You guys don't know your stuff 8p.

Despite what Jaivaz states, Dattebayo actually translates to "don't ya know?" And is commonly tagged onto sentence or more commonly a statement to add meaning, or just to sound cute.

In the Japanese versions, Naruto often ends his sentences with "dattebayo" or "(verb)-ttebayo", and as such Naruto has a unique style of speech. In the Japanese language, an ending can be added with no meaning to make the tone sound more tough, childish, girlish, or many other changes depending on the many existing endings. "-ttebayo", which is not a well-known ending, has no literal meaning and cannot be translated, but carries the connotations of the speaker being uncultured, brusque, and seeming tougher than they really are.In the English anime and video games, he often says "Believe it!" to fit with the mouth flaps of "-ttebayo".

Despite what superking said, Jaivez was completely right. Dattebayo has NO actual meaning and is just tagged to the end of narutos sentences, its just like his dialect.
Naruto's style is '(verb stem)tte bayo!' For instance, wakattebayo is "I get it already" or nan dattebayo is "What (the heck) is that?"

Directly derived from an actual interview with the creator himself, Masashi kishimoto.
(Quote)
- Is Naruto's favorite phrase, "dattebayo" modeled on anything?

K: That isn't really modeled on anything either. When I thought of childlike
speech, "dattebayo" instantly came to mind. It's like it's become a part of
Naruto, and even now it brings out his "mischievousness".
(End quote)

I guess it's just up to fans to determine for themselves what it truly means...