This is not some new slang. It's a phrasal verb that has been around forever.
From UsingEnglish.com:
Play at - Pretend to be something
Example:
He just PLAYS AT being a lawyer- he never wins a case.
http://www.usingenglish.com/referenc...s/play+at.html
It is also used, as mariaklec said, to pretend to be doing something. It's similar to "plays like", as in, "he plays like he is a lawyer". Again, as mariaklec says, not the most formal way of saying something but certainly acceptable and understood in everyday language.