Masochism. Bob Flanagan used to hammer nails through his penis and it was classified under "performance art". This fellow chose needles. But why? Here's Flanagan's answer.
http://en.wikipedia.org/wiki/Bob_Flanagan
http://en.wikipedia.org/wiki/SICK:_The_Life_&_Death_of_Bob_Flanagan,_Supermasochist
http://en.wikipedia.org/wiki/Bob_Flanagan
http://en.wikipedia.org/wiki/SICK:_The_Life_&_Death_of_Bob_Flanagan,_Supermasochist