How to train readers in Argot or Slang
I have a character which is typical street thug, criminal and did his time in jail. He is using a lot of underground Argot and thug slang. Example below
At the end we got the ice, gravy train if you know your beeswax
In translation from argot it means "At the end we stole the jewelry, easy money if you know what you are doing"
What is a good way to explain these expression to a reader without info-dumping or interrupting flow of the dialogue. I would like to lessen the learning curve for the reader to learn desired argot/slang or find an effective way how can reader understand uncommon expressions specific only for certain group of people (prostitutes, criminals, cops, bankers etc.)