I friend was reading a Herman Wouk novel (don’t remember the title, but I can find it if there’s any interest), and in one passage, there are several references to someone dressing like a “Deke.” A cursory Googling didn’t turn up anything meaningful.
Right. It’s his semi-autobiographical novel about a Jewish kid from New York who becomes a writer. The references to Dekes comes from when the character is in college, and it’s talking about the frat:
Then there’s a scene where he dresses like a Deke, only to realize later, when he runs into an actual Deke who’s a friend of his, how un-Dekelike his clothing really is, and he’s embarrassed that he even tried it.
Another vote for this, with a citation from the Cassell Dictionary of Slang, which lists a nineteenth century origin for the term. It’s apparently also ice hockey slang for a feint, from “decoy” [attested from 1960], but that really doesn’t suit the context.