I believe that slang is where a language starts to develop itself, independently and deliberately. The small danger here is that "slang" cannot be universally understood (which is why I advise learners not to use it), and is often used to mark cultural territories. Just saying that something is "slang" is a very misleading comment about when, where, how or even IF a phrase could be understood. Even if it is understood, it could be interpreted as invasive if you're not actually from that "group". Aside from that, as a concept it's very poorly-defined.

I don't think slang "ruins" a language. That is how languages evolve. It has been happening in all languages since the beginning of time. much of the "standard" English today would be considered "slang" in previous time periods.

Who cares.

"I don't think slang "ruins" a language. That is how languages evolve." - exactly. Arucard303, did you hear about 'Newspeak' (a fictional language in George Orwell's novel 1984) or 'Basic/Simple English'? Simplify the language is dangerous. Slang enriches the language.

Yo, it no be no nuttin' ya'all can do 'bout it! :P