What is funny?

I find videos that criticize others, whether they are politicians, celebrities, or even everyday people. I find it funny because they mock others using different types of humour, and they given very funny opinions of that person. Also, most of the times what they state is very true, although sometimes it is exaggerated. There are many people on youtube that post such videos, and my favourite person is a comedian called David So. Once every few weeks he posts videos, making fun of different people everytime. An example of his video is the one where he talks about a girl that posted a video about asians people in UCLA(http://www.youtube.com/watch?v=lOGpGoEMu2s). Although he isn't very well-known, I still find his type of comedy very humourous, keeps me waiting everyday for a new post.