What is the easiest way to make graphs like these?
Is there an app for it?
Google Charts allow you to dynamically generate images similar to those. But it takes work obviously to put all the data points down.
They have a web app to make chart generation easier.
But if you want that specific look, it is pen and paper for you. And you better have drawing skills.
On the other hand, if you are talking about that humor style, you may want to check GraphJam
I'm not sure if that's what you're looking for, but there's Google Trends. It shows you a graph of the average traffic of a set of phrases/keywords versus time. An example of what you can get is: http://www.google.com/trends?q=runescape,+world+of+warcraft