Do you know ghouls from goblins and ghosts?
pet form of masc. proper name John (see -y (3)). Used as a contemptuous or humorous designation for some class or group of men from 1670s (e.g. the typical name in the North and the Northern armies for a Confederate soldier during the American Civil War). In the Mediterranean, it was a typical name for an Englishman by c.1800; in the Crimean War, it became the typical name among the English for "a Turk," later extended to "an Arab" (who by World War II were using it in turn as the typical name for "a British man"). Johnny-come-lately first attested 1839.
johnny john·ny (jŏn'ē)
A loose short-sleeved gown opening in the back, worn by patients undergoing medical treatment or examination.