Kaiserschmarrn is also spelled Kaiserschmarren. Kaiserschmarren only denotes the dish and has no idiomatic meaning. The word Schmarren (alternative spelling: Schmarrn) is (a) short for Kaiserschmarren (b) has the idiomatic meaning "nonsense, rubbish"
This is very popular in Slovenia, where it is called šmoren (from the German word Schmarrn), or more formerly cesarski praženec, a calque on Kaiserschmarrn, meaning something like "the Emperor's pancake" (for a recipe, see http://www.austria.info/uk/austrian-cuisine/kaiserschmarren-1561302.html). According to the Slovene culinary website www.kulinarika.net, this treat got its name when an innkeeper in Ježica served it to the Austrian and Russian emperors, who were stopping there on their way to the 1821 Congress in nearby Ljubljana (Laibach). Today Ježica is part of Ljubljana, and that same inn, or gostilna, is still there; it is called "Pri ruskom carju" ("The Russian Czar"), and it has lent its name to the surrounding neighborhood: the Russian Czar neighborhood.
Misspelling of a south German dish, loved by children: Kaiserschmarrn - a kind of pancake, destroyed in the process of frying, then served with sugar powder and often with apple sauce. I dunno' if it is used as idiom for something. Could be worth it.