They laugh at it of course. What else can you do about a "currency" invented by an unknown entity, loved by videogamers and whose total circulation is below the GDP of mongolia?
BitCoin's 1000% rise in 3 months would seem to put it well outside the traditional conception of stable. Keep in mind, since the benefit of currency stability is to protect both buyers/borrowers and sellers/lenders, a rise is as damaging to stability as a fall (just impacting a different segment of the transaction).
While there are a few examples of fiat currency experiencing hyperinflation, it's almost always been the result of extreme political uncertainty. In a normally functioning political environment, the change in currency value may still be significant, but tends to be fairly stable (even if it changes, it changes within a predictable range).
That's clearly not the case with bitcoin.