to turn down means to reject or to decline. as in "I turned down his invitation." So,"turn down for what" means "Why did you turn it down?" turn down for what" = simple speech only for conversation

This is a song by Lil Jon, right? The internet reliably informs me that 'to turn up' is slang meaning 'to party.' I had to look that up, it's not a common usage in the UK. So 'turn down' would be the opposite of that. So 'turn down for what' would seem to be a defiant statement. Stop partying? What for?

I know that there is a song with this phrase but I don't know what does it mean too :D