Title text: I'm only willing to visit placid lakes, salt flats, and painting exhibits until the world's 3D technology improves.
This comic is probably a reference to the new Nintendo 3DS handheld video game system that has a 3D effect if you put your head in the right place for the handheld device. Also, it is a reference to the proliferation of 3D movies. The 3D movies and 3D games make your eyes work harder which can cause headaches in some.
In this comic, Cueball is using the excuse that 3D gives him a headache to get out of going outside into the real world, where everything is in 3D. Instead he stays inside and looks at his 2D computer monitor. In the image text, he says he will only go to places with little 3D motion.
On a side note: Megan is wearing her helmet and practicing safe bike riding. Way to go Megan!
This comic was released on April fools day. The April fools joke for 2011 made every comic on the site 3D, thus forcing people like Cueball to endure 3D even at their computer screens. The 3D view is still available at http://xk3d.xkcd.com/.
- [Megan has a bike, and is wearing a helmet. Cueball is at a computer.]
- Megan: Wanna go for a bike ride?
- Cueball: Nah, I hate 3D stuff. It gives me a headache.
- When you think about it, this excuse can get you out of almost anything.