I'm not unemployed, i'm working right now. A "Devil's Advocate" is one who can see both sides of an argument and will debate thusly. If two people are having an argument, a third (and neutral) party may well intervene and say "Let me play Devil's Advocate", he will then argue both sides with no vested interest. From Wiki: In common parlance, a devil's advocate is someone who, given a certain argument, takes a position he or she does not necessarily agree with, just for the sake of argument
The origin of Devil's Advocate comes from the process of making someone a saint. If the church put someone up for sainthood, the Devil's Advocate would dish all the dirt he could find on the person and present the strongest argument he could for why the person shouldn't become a saint. In that sense, he was the taking the Devil's side.