IIRC, this happened on his first day. Short version: He was overheard by Walt Disney’s brother while he was (for an audience of several Disney employees) doing an impression of what a porn film starring the major Disney characters (Mickey, Minnie, Doanld, etc.) would sound like. By the time he reached his car with his belongings, there was already a maintenance guy changing the name on his parking space.
This tale was told by either Robert Heinlein (in “Expanded Universe”) or Larry Niven (in “Playgrounds of the mind”) and since I own both, I’ll try to find it. It’s probably Niven, he collaborated with Ellison on some projects in the Seventies.
I’ve heard the story from Harlan himself. I think he said they’d hired him to work on “The Computer Wore Tennis Shoes.”