What is Xkcd?
1. Saving a few seconds at a long red light via elaborate and questionably legal maneuvers.
2. Having someone call your cell phone to figure out where it is.
3. Calling the Ackermann Function with Graham's Number as the argument just to horrify mathematicians.
4. Instinctively constructing rules for which floor tiles it's okay to step on and then walking funny ever after
"That is so XKCD."
An online comic strip catered towards geeks/math majors/etc. Makes the fatal flaw of assuming that because it has a niche audience, it will automatically be funny. On the contrary, it is rarely amusing, and is only popular due to said audience's lack of recognition in most mediums.
"The vector of c is 5."
"Hahah! I think that that comci, xkcd, is funny because I automatically approve of anything nerdy. I also love the dick."