So someone asked me what Bumbaat in Ladki tu hai badi bumbaat means. Well, as far as I know there is no such word as Bumbaat in Hindi or any other nearby language. But then I easily guess what bumbaat here means.
Most probably bumbaat is a deformation of the word Bombard, and the meaning here is for a Bombardment, or simply a Bomb. The meaning seems to fit the song and the line quite well, so I guess this should be it. Still, if you have a clear idea of something that is bumbaat and should fit here, you're most ooh la la. Oops, Welcome.
Update: It seems Bombaat is a Kannada word meaning very good, or awesome. Thanks to comments from Lokesh, AJ and Suhas.