I think J. K. Rowling pulled a fast one on us. Let me explain:
My mission requires a lot of searching through the library’s reference section. While scanning over a row of specialized dictionaries, one caught my eye. It’s title was Jazz Talk1. As I guessed, it was a slang dictionary with a special focus on people who made up the ‘jazz culture.’ Of course, the first thing that came to mind was the jive-talking scene from Airplane! I thought it would be funny to make a literal translation of that scene, so I printed out a transcription of the dialogue. To my disappointment, the slang from the movie was in some cases too general to warrant inclusion in the dictionary, and in others made up entirely. Yet in my search I came across something surprising. While looking for ‘mofo,’ I found this:
Muggles [etym. Unknown; some currency among jazzmen from c. 1925 – c. 1945, rare since; see also BOO, GAGE, POT, TEA]
The word ‘muggles’, it seems, has a bit of history to it. I decided to investigate further. The Cassel Dictionary of Slang2 had what I needed to know.
muggles/muggie n. [1920s-70s] (orig. US drugs) 1. A cigarette with marijuana (occas. hashish) substituted for some of the tobacco and pushed back inside it; thus muggled up, intoxicated by marijuana, muggle-smoker, a marijuana user 2. A smoker of marijuana.
When asked in an interview, Rowling said: I was looking for a word that suggested both foolishness and lovability. The word 'mug' came to mind, for somebody gullible, and then I softened it. I think 'muggle' sounds quite cuddly. I didn't know that the word 'muggle' had been used as drug slang at that point... ah well.3
Then again, as others have pointed out, there’s a lot of innuendo and implied naughtiness in her books. I will not go so far as to say that Rowling was untruthful in her interview, but consider the backlash if she said that it was based on the slang term.
As an aside, as I was searching for ‘muggle’ in the Cassel dictionary, I found a few delightful euphemisms.
Much goo about nothing n. masturbation
Much-travelled highway n. [19C] a large and loose vagina
Muddy funster n. [20C] a euph. for motherfucker
1. Gold, Robert S. Jazz Talk. New York: Bobbs-Merrill Company. 1975.
2. Green, Johnathon. The Cassel Dictionary of Slang. London: Cassel. 1998.