Taxing the hell out of it would work. What company would want to pay 90% of their cryptocurrency in taxes? and if you can't pay your taxes in cryptocurrency, and instead have to convert it to cash, that'll drive the price down pretty quick and make everybody scatter.

edit: to head off the downvote brigade, I'm not advocating for this. Only pointing out that "banning" doesn't necessarily mean outlawing its use, but can also include making it unfavourable to use.