never heard of this before.......
"Rosenmontag (Rose Monday) is the highlight of the German "Karneval" (carnival), and is on the Shrove Monday before Ash Wednesday, the beginning of Lent.[1] The "Mardi Gras," though celebrated on Tuesday, is a similar event. Rosenmontag is celebrated in German-speaking countries, including Germany, East Belgium, Austria, and Switzerland, but most heavily in the "Hochburgen" (carnival strongholds), which include the Rhineland, especially in Cologne[2], Bonn, Düsseldorf [3], Aachen and Mainz.[4] In contrast to Germany, in Austria, the highlight of the carneval is not Rosenmontag, but Faschingsdienstag (Shrove Tuesday)."
From the pictures it looks like they have fun.
Rosenmontag in Deutschland: Putin als Tänzer, Brüderle als Straßenköter « DiePresse.com
German Carnival Peaks With Rose Monday Processions - SPIEGEL ONLINE