"Le petit déjeuner" is the breakfast in French. "Le déjeuner" is properly the lunch around midday. Saying "le déjeuner du matin" is indicating you are speaking of breakfast, as opposed to lunch.
The song "Du hast" by the band Rammstein is a bit of a word game. When one hears the lyric "Du hast" (from the German verb "zu haben" (to have), the first thought is, that the singer is trying to say...