Anyone can do it by bid whacking with small orders. Some even post disparaging remarks to go along with the bid whacks. Once the price gets walked down they buy back in with larger orders. At least that is the MO but it doesn't always work that way or they make less then a long does by staying in.
The best example is the video Crammer did about how he would go about shorting a stock when he ran his hedge fund. The video was so incriminating it was pulled.