From Wikipedia (http://en.wikipedia.org/wiki/United_States_Patent_and_Trademark_Office)
U.S. Patent 6,368,227, "Method of swinging on a swing", issued April 9, 2002 was granted to a seven-year-old boy, whose father, a patent attorney, wanted to demonstrate how the patent system worked to his son (aged 5 at the time of the application). The PTO initially ...
To answer your first question, whether this is a joke or not, see the last paragraph, which states:
Lastly, it should be noted that because pulling alternately on one
chain and then the other resembles in some measure the movements one
would use to swing from vines in a dense jungle forest, the swinging
method of the present invention may be ...