Takipayanaku, must be some idiom place, because challa are a few celebrations as Carnival held in the North of Argentina, Bolivia and other Andean countries. And in Chile, told challa to a bucket flat wearing the gold diggers in the rivers, is the bucket that move circularly to "wash and that remain below the pepeitas. But the most known is Carnival of the northern provinces, because a great fiuesta with water is paper and flour. Who knows which meaning give locals if they say "don't be challa". I live in Buenos Aires and I know many idioms of the Spanish American countries but I do not know that.