Cannon Randy is a Halloween-themed episode from the comedy series How I Met Your Mother. It was originally broadcast in the United States on November 1, 2010.
On Halloween night, Ted (dressed as a hot dog), Barney (dressed as Johnny Lawrence from The Karate Kid), Marshall, (dressed as a bull), and Lily (dressed as a matador) all go to a Halloween party, hosted by Goliath National Bank. Their friend, Robin, however, does not come to this party. One of Marshall's employees, Randy Wharmpess comes, and asks where Robin is, seeming very interested in her. Lily tells him that she went to a different party, but may come later. Randy then asks them if they are watching the Halloween parade, and Ted tells him he is, but it is soon revealed that Ted is not talking about the official parade in The Village, but the "Post Halloween Walk-of-Shame Parade" which takes place the next morning, while people are walking back home after a night of hook-ups.
While watching this "parade" they notice Robin coming home, dressed as a maid. Lily, believing that Robin slept with a man the previous night, tries to figure out who she slept with. She asks Robin a few questions, and eventually comes to believe that Robin slept with Randy, Robin admits this to be true.
Later that day, Lily is talking to Randy, and Randy tells her that he has never slept with Robin, except for in his dreams. Lily confronts Robin about her lying, and Robin tells Lily the truth, that she did not actually sleep with anybody. She actually filmed a commercial about adult diapers, and was too embaressed to admit that to them.