Simply question:

Is this gramatically correct? (I thought no, cause 2 negatives in one sentence are not allowed in English. Or? Its a question of bet, but I found smt. similar on wiki and it looks I've lost :( )

Ain't no buddy. 

And what does it mean if yes. 

Thank u for replay.

Hi Phesant, and welcome to English Forums.

I think "ain't nobody" is quite a bit more common than "ain't no buddy" - and means simply "no one" or "nobody."

No, it's not grammatically correct, but you'll hear it in songs and in non-standard conversation all the time. (Ain't isn't correct either, and the double negative just makes it more colloquial.)

There's no point in knocking on the door. You can see there ain't nobody here.

(PS: Thank u for replay = Thank you for your reply.)