This song was a tribute to one of the band members that was killed in a car crash. That is why they say that there "Back in Black: becasuse when someone dies you were black. When they played this song at the tribute concert they performed all dressed in black. Hense the song name "Back in Black. If you go to google and serch the histor of this song it will explane in greater detaile. This song has nothing to do with the band being happy or him wearing his favorit black shirt.