the Monkey was originally a kids’ ride at Honda’s Tama Tech amusement park near Tokyo.
It became an unexpected hit with adults too, and the name Monkey stemmed from how grown-ups resembled circus gorillas when perched atop the small bike. Honda saw a sales opportunity and began selling them to the public.
http://japanesenostalgiccar.com/video-watch-james-may-put-together-a-honda-monkey/#more-55424
Thanks Marc!