Many people are possessed by demons. Those around them don't know it. This is one such person. They generally hurt others or hurt themselves. They are trying to evoke a response of disgust, fear and revulsion. This man has given up his consciousness and free will long ago. He no longer even exists. The demon inhabits his empty husk and animates it.

He's doing it for attention, and nothing could be funnier than him doing this without receiving any recognition