A lot of people do not really like 3D movies. But with many new movies, seeing them without 3D isn't really an option. Enter 2D glasses, which strip the 3D out of 3D movies for your viewing pleasure.
Here's how they work, from the folks behind them:
When you watch a 3D movie, there are actually two images being projected onto the screen. That's why the screen is blurry when you look at it without glasses. In 3D glasses one of the lenses blocks one image and the other lens blocks the other image.Brilliant, right? Well, if you want on board, you can get your own pair of 2D glasses for $10, shipping included. (By the way, ThinkGeek totally called these back during April Fools'.)
Thus, when you watch a 3D movie each of your eyes is seeing a slightly different image. Your brain combines those images together, creating the illusion of a 3D image.
2D Glasses block the same image with both lenses, so each eye gets the same picture resulting in a 2D image and an elimination of eyeball strain.
Via 2D Glasses