Colonel Kurtz and AJWest have both made some excellent points here. The only thing I would add is you need to be careful, when using any object to defend yourself, about showing any signs of prior intent. For example if you have a RIF under your bed and bluff someone, but tell the police you had it under your bed "in case you needed to defend yourself", you're showing prior intent to cause harm and/or fear. You open yourself up to a whole world of potential problems there, and that goes for anything. Weapons of opportune are, as Kurtz and AJWest have said, perfectly acceptable so long as you can justify their use and that you genuinely felt that your personal safety was in jeopardy.
To answer the original question, not sure I would use a RIF to defend myself, unless it was to hand and I had no other options, in which case I'd use it as a club rather than trying to pretend it was real. But I can;t see any circumstances where that situation would arise to be honest.