It means, well...if I am alreayd f*****up, then I will continue on what I am doing, don´t matter what.http://pt.urbandictionary.com/define.ph ... n+for+what
It´s a rebellious way that (some of) the young expresses themselves, as if saying I have lived 18 years on this earth, I ought to make my own decisions! ...and every time my parents or society is going to tell what I do, it will make me more rebellious!
It´s a bit of the old what´s done is done..
Many of us will have our fifteen minutes of rebellion, and some will be lucky enough to survive it!
Perhaps the music was what triggered the fad of the catchphrase/slogan of sorts, but its origins could well be traced to some young with the volume turned up, or to do with the habit of "turnt up" (getting crazy/acting crazy etc).http://www.urbandictionary.com/define.php?term=Turn+Up
It doesn´t matter anyway, the fact is, it got synonymous with "who are going to stop it?"