so should i short Groupon then?

My problem with selling short has always been that I don’t control my time horizon; the person who has lent me the shares does. After all, even if you are right in your assessments of value, you will not make money until the market corrects its “mistakes” and that may take weeks, months or even years.

Aswath Damodaran on selling short the stock you perceive as overvalued