Slang is very common in everyday speech. Almost every group, organization, and society has their own "lingo", which makes sense to them, but not necessarily to others. The Italian mob is no different.
If one were to rent movies dealing with Italian Gangsters, such as: Good Fellas, or any of the three Godfather movies, they would find many slang words they may not understand. Some of these words are used in place of other words, like the joint, which means prison, or junk, meaning drugs. Whereas other words have their own meaning such as, a made man. This is a man who has extreme importance and cannot be killed without permission. The made man has so much stature that if he is killed the man who killed him will also be killed for sure.
Some of the "gangster" words are now used in every day speech such as enforcer, the man who does al the "dirty work"; knock off and take care of ,both meaning to kill; and doing hard time, which is being behind bars or in prison.
These words have become commonplace. It is also possible that they were commonplace and "the Mob" sort of took them as their own.
There are also saying used by gangsters to explain things. If a man steals a large sum of money and is questioned by the police, he will tell them that he won big playing craps in Vegas. The police are obviously natural enemies of the Wiseguys, gangsters. They are always trying to make the big arrest, but the wiseguys use lies such as the one about craps to keep from being pinched, or arrested.
Inside the mob there are separate groups known as families. These families all have a leader known as the Don. This man takes Don as his first name. So Tony Bonelli becomes Don Bonelli. This man can also be called the Godfather; this is obviously how the title for the movies came about.
These godfathers often protect people who feel they can't go to the police for help. In return for this protection they ask for favors. These favors can range from killing someone, to hiding a gun, to giving the godfather some fruit for free.
When the wiseguy was selling some junk he got pinched. His first night in the joint he got whacked. Since he was a made man his family had to retaliate. Soon there would be an all out war on the streets of New York. The Dons of all the families met to try and find a peace, enough blood had been shed. When Don Bonelli's enforcer, Anthony, started "suggesting things", all of the other Don's fell in line and decided to stop fighting and have a peace. The killing stopped soon there after. The police thought they had stopped, little did they know, they had no control in the city.
This was a small example of how some of the "gangster slang" could be used. If one were to hear that without any background information they would be extremely confused, and wonder what the speaker meant. So it is necessary to know some of the lingo to fit in and understand. This goes for all slang, not just that used by the Italian mob. If you are not part of the group that uses the slang you will probably not understand it. It may take a while to learn all of the slang used by any particular group, but with a little observation it can be done and anyone can understand what is being said.