Apparently, Dortmund are planning a new visitor's center (very much like the one Bayern has at the AA), which will be called Fanwelt (Fan-world).
In their new winter catalog, they advertise for it with the heading "Die Südtribüne gibt es natürlich auch in der Fanwelt", meaning "The Südtribüne is naturally also present in the Fanworld", along with a mockup of the center, and a background of what appears to be fan choreography, all in yellow, from the Dortmund faithful. Looks good, right?
The only problem is, the choreography is actually from FC Bayern's Südkurve fans, during last season's DFB Pokal quarterfinal against Dortmund, where the Bayern fans first displayed the colors of the city of Munich (which also happen to be yellow and black), with the words "The colors of the most awesome city", and then switched to red and white, with the words "The colors of the best club".
Needless to say, Dortmund is being ripped from all sides, and have already apologized for the hilarious mistake.