I wondered about his history of suing people and found this article in the Atlantic. He sure isn't shy about dropping lawsuits on folks.
http://www.theatlantic.com/national/archive/2013/03/the-lawsuits-of-donald-trump/273819/
http://www.theatlantic.com/national/archive/2013/03/the-lawsuits-of-donald-trump/273819/