finnegan pin
n.— «Finnegan pin…A nonexistent object used as the basis of practical jokes.…A finnegan pin in the muffler gear.» —, 1968. (source: Double-Tongued Dictionary)
Further reading
The adjective corny describes someone or something “unsophisticated” or “naive.” This sense of corny goes back at least as far as the 1920s. Seed catalogs of the time often contained bits of goofy jokes and broad humor...