Poisson
Permanent link to this comic: http://xkcd.com/12/
Image URL (for hotlinking/embedding): http://imgs.xkcd.com/comics/poisson.jpg
[[A stick figure says to another black-hat-wearing figure.]]
Man: I'm a poisson distribution!
Man: Still a poisson distribution.
Hat Guy: What the hell, man. Why do you keep saying that?
Man: Because I'm totally a poisson distribution.
Hat Guy: I'm less than zero.
[[Man is gone; Hat Guy is whistling.]]
{{alt text: Poisson distributions have no value over negative numbers}}