Go buy 5% of nxt (will cost you 1 million dollars -- if prices don't go up while you are buying that many nxt) then come back here showing the "attack". If you succeed, the prices will drop and you will lose your 1 million dollar investment. That's the problem with these "what if" scenarios. They are not practical. People who have that much at stake have an incentive to protect the network without any shenagginings. It's in their own best interest to protect the network. That's why it's called proof of stake.
One cannot attack Nxt that way even if he is unreasonable and do not care about the money.
Perfect crime. Spend several billion dollars, buy 90% of all coins and try to destory the currency. Maybe in ThePurplePlanet's Universe it sounds normal. Or maybe he should just take care of his mental health a little better.