Sirius XM Radio is having an interesting year. The satellite radio operator’s share price is down 88% in the last 12 months, but up 204% in 2009. Why the volatile ebb and flow?

Part of the reason is the company’s high profile on Wall Street – it’s arguably the most popular penny stock out there. And why shouldn’t it be? After all, the company is the exclusive provider of satellite radio and in-car TV broadcasts for almost 20 million paying subscribers in the United States and Canada.

But to assume that all the interest in Sirius XM (NASDAQ:  SIRI) is because of the company’s great growth prospects would be dead wrong. Scores of investors want to see this company crash and burn.

As of last month, almost 5% of shares available to the public were short Sirius XM, and while that might not sound like a lot of shares, it’s 25%