Sorry to tell you, but Joe is a masher. Also, he’s messing around with dynamite! Now, will you kindly hold my roscoe? A g-man is headed this way.
Lost? Check out this online American Slang Dictionary to decipher what I just said 
When writing urban fantasy, usually language and slang is a no-brainer since the setting is usually a contemporary city or even one in the future. However, if your story’s set in a city but in a not-so-contemporary time, what then? Well, let me tell you, there are words used in the 1940s that are still used today, and words that I had to do a double-take at and scratch my head over.
Don’t worry though, I didn’t litter the story with obscure slang, but it was definitely fun using a word here or there (ooh, is that verisimiltude? 
). For example, when you wanted to call someone CRAZY, you’d say “psycho” or “berzerk.” A bar was a “gin mill,” and if you wanted to call a person stupid, he or she was a “meatball.”
If your urban fantasy encounters the same thing, don’t be afraid to use the slang of the times–but balance it out so that it doesn’t detract from the story or its flow.
I’m an ’80’s kid, so I still catch myself using a phrase that would make teenagers go “huh?” Even worse, I remember all the dance moves too, so those just make my family laugh at me.
Ok, back to writing…