I only just watched this thing today and it is pretty crappy. I mean if you don't like the new Top Gear why in the hell would you make a video where Hitler of all people agrees with you?
Because it's an internet meme generator thing; there's a website to easily generate them. There's loads of examples going around - here's an article in the Telegraph in 2009 citing the best 25.
I agree this one isn't particularly funny. Though most aren't really.
Because there's a website where you can turn that clip into any sort of rant you want via the subtitles.
Most of them aren't funny alright. Maybe it's worse for me because I can speak German, and so the subtitles are clearly nowhere near related to what's being said.