That’s the thing about slang, it rarely actually gives you totally new meanings. It usually just gives you less formal and deliberately impenetrable-to-the-outgroup synonyms for existing words.
A whole lot of words in any given language do not provide a totally new meaning from other words in the language, but exist to allow for varying connotations. Compare the words "childish" and "childlike", for example. They mean the same thing, "in the manner of a child", but have negative and positive connotations respectively.
