You get this title by joining one of the four (Bishop/ Mordino/ Salvatore/Wright) mafia families in New Reno and having more than 4 Intelligence. For each mafia family there is a chain of quests, upon the completion of which you become a Made Man of that family.
You can see the special stock and get discounts at the New Reno Arms.
You can paralyze Jagged Jimmy J when you have Intelligence less than 4 and when you want by choosing the line "How can one TRULY know another, Jimmy? Is it even possible while we are on this mortal coil? Or is it only possible when we free ourselves from our physical bodies?"
Strangely, the sentence for paralysing Jagged Jimmy J when you have IN < 4 it's not a normal sentence (normally poorly constructed and difficult to understand) said by a low-intelligence character and looks like more something that an intelligent character could say.