This website defines "narishkeit" as follows (my copy of Leo Rosten is temporarily displaced due to minor construction):
Narishkeit: (nar-ish-kite) foolishness (a nar is a fool) "An artist, you want to be? Never mind this narishkeit! Better you should go to college and get a real job!"I mention this because I was thinking the other day that perhaps it comes from "na'ar", which is Hebrew for youth. In other words, youthful foolishness or nonsense.
Linguists, what say you?