What happened 

Shares of Clean Energy Fuels (CLNE 4.26%) dropped as much as 20% in trading on Thursday after a big shareholder revealed a sale of stock. Shares of the energy stock are down 15.2% at 3:20 p.m. EDT. 

So what

Total Marketing Services, which now holds 26.7% of Clean Energy Fuels' outstanding shares, revealed that it sold 1.25 million shares earlier this week. Total Marketing Services has been selling shares for a few weeks, so the sale isn't entirely surprising, but when large shareholders sell a stock it can be seen as either a lack of confidence in the company or a view that shares are overvalued by investors. 

Natural gas truck on the road.

Image source: Getty Images.

In addition to this share sale, Clean Energy Fuels itself sold 10.5 million shares on June 8, for proceeds of $100 million and has now sold 22.8 million shares and raised $200 million since the May 10 at-the-market equity offering program was announced. If the company itself is taking advantage of the higher stock price this week investors may have been too optimistic in pushing shares higher.

Now what

Earlier this week, Clean Energy Fuels seemed poised to become the next meme stock on Reddit, but those hopes may have been dashed today. Insiders and Clean Energy Fuels itself are quickly unloading shares after the rise in the stock price and traders are taking notice. Meme stocks can rise quickly and fall just as fast and investors are seeing the downside of the meme trend today.