麦 is short of 麦克 麦克风, 麦克 or麦克风is microphone 。
u know its necessary to have a phone when u KTV 、 give a address or make a TV show 。
没麦 or 没拿麦 is that without a microphone in him ,so he cant speak or sing 。 and 没麦 is use widely in chinese chat room or chat on video。