"Leck mich im Arsch" is a canon for six voices attributed to Wolfgang Amadeus Mozart. The title's literal translation from German is "lick me in the ass" (or, idiomatically, "kiss my ass"). His publishing company distributed a much tamer version, big goddamn surprise, with the title changed to the more pedestrian "Laßt froh uns sein" ("Let us be glad!").
The article goes on to mention that recent research has shown that the song was probably written by some guy named Wenzel Trnka, but since that version doesn't help put Amadeus into context, I personally choose to ignore that part.