The Spanish slang of the Buenos Aires underworld which is common in tango lyrics and terminology
(from batango.com (http://www.batango.com/Loomis.htm))
Lunfardo, the slang of Buenos Aires, is innately connected to tango; both were born in the same setting, of the same people, and for similar reasons. Lunfardo, like tango, is a hodgepodge created by poor immigrants searching for identity
(from tangonoticias.com (http://www.tangonoticias.com/articles/a2004/aug/lunfardo.htm))
This originated terms and expressions that formed a new language, that of thieves and jail inmates. The secret tongue of "lunfardos", term used by thieves to refer to themselves. In this way watch became "bobo" (dumb-stupid) due to two characteristics, it is very easy to steal and it works all day long non-stop. Lunfardo is rich in Italian dialectal terms and also French words.
(from totango.net (http://totango.net/terms.html))