You're never truly down with the local lingo, unless you pick up the slang. This is probably never truer than in Argentina, where they speak Spanish like no other. I'm considering buying this Argentine phrase book, Che Boludo, just so I can try to fit in.
The title, "Che boludo", is the most Argentine of phrases. If you can say it naturally, and don't sound like a try-hard tourist, it's the ultimate linguistic success.
As soon as you become aware of this phrase, you hear "boludo" everywhere you go.
It was while on my quest to learn more Argentine slang words that I came across an interesting podcast teaching Spanish swearwords. Sorry to lower the tone, but it did make me laugh aloud - less for the words themselves, more for the American guy's translations. Even if you don't speak Spanish, it's worth a listen. Note how the Spanish speakers remain "tranquilo", while the American translator starts off calmly and then gets a little too into it. Is he a frustrated actor or just plain angry? You'll soon see what I mean.
To hear it, click on the audio player on this page of LearningSpanishBlog, under subheading of "Learning Spanish like crazy".
Bambino Pons, as he's nicknamed, is famous for his singalong commentaries, which often include background music. Here's an internet "best of", where highlights include singing Dennis Bergkamp to the tune of We Will Rock You. Note the slang in the YouTube viewers' comments: "Es una boludez que me mata de risa!!" - "It's boludo (here meaning 'silliness') that makes me die laughing."