Keyboard Crasher: AKA Angry German Kid
Another subject that is very popular on Nico Nico Douga, the Japanese take on YouTube, is "Keyboard Crasher." He is known to English-speakers as "Angry German Kid." Here is the original (translated) video:

Note: This is acting. Go to the video page for all the details about him and this video.

This video got incredibly popular among the internet crowd, and like many foreign video clips (to both Japanese or Americans), they tried to pick out words in their own language, often ending in hilarious results. (Continued after the break.)

As the Japanese started digging funny phrases out of his German screams, they began remixing the video to various songs, from Hardcore to Denpa. Here are a few examples:

Follow the links below to find many more videos of this type:
[YouTube search]
[Nico Nico Douga search] (Registration needed)