Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 265
Other / Unknown
Flight Deck / Cabin / Aircraft Event Other / Unknown
General None Reported / Taken
Human Factors
We had an FAA Inspector show up to the cockpit that exhibited suspicious behavior and was not in compliance with our jumpseat dress code.  He asked the Captain if either of us was an FFDO and then confirmed 'so there are no weapons on the flight deck; correct?'  I've never been asked that question by an FAA Inspector.  He took copious notes throughout the boarding process.  Again; very unusual.  While the Captain was in the terminal he mentioned 'The Captain seems like a very serious man.  Was he in the military?'  I'm not sure what the Captain's flying background (or mine for that matter) has to do with our execution of a safe flight?  After talking with the Operations Center; we were directed to allow this individual to board 'or be suspended.'  We departed.  This individual clearly demonstrated suspicious behavior during boarding as explained in the Operations Binder.  I am now confused on the extent of a Flight Crew's authority to deny boarding based on a perceived threat.With all the distractions of a very unusual jumpseater; we failed to recognize this individual was not in compliance with the facial hair policy for Jumpseaters found in our Operations manual.  If this individual had needed his oxygen mask in flight with a very large beard that would have been a valid safety concern.  Does our jumpseat policy apply to FAA Inspectors?
Air carrier First Officer reported an FAA Inspector requested to ride the jump seat for a line check.