CAPT FAILS TO DON OXYGEN IMMEDIATELY WHEN FO LEAVES HIS SEAT.

Narrative

AT 31000 FT I INSTRUCTED FO TO GO TO CABIN TO INSPECT LOOSE OVERHEAD PANEL. I DID NOT IMMEDIATELY GO TO OXYGEN. FO AND I ARE RESERVE PLTS. WE WERE CALLED TO THE ARPT WITH VERY LITTLE TIME TO GET THERE. ARRIVED 15 MINS PRIOR TO SCHEDULED DEP. FAA ACR INSPECTOR WAS WAITING. PREPARED ACFT (FO ARRIVED 5-10 MINS PRIOR TO SCHEDULED DEP) AND DEPARTED ON SCHEDULE. FLT WAS SHORT 57 MINS ATL-DAB. ON TKOF GOT WARNING LIGHTS FOR REVERSER LOCK PROB. CLBOUT WAS BUSY AVOIDING BROKEN CUMULUS CLOUDS. VERY BUSY TALKING TO COMPANY RPTING PROB. AT CRUISE FLT ATTENDANT CALLS ABOUT OVERHEAD BIN COMING DOWN ON PAX. I INSTRUCTED FO TO RETURN TO CABIN AND CHK. AT THIS TIME I TURNED TO WATCH FAA INSPECTOR GO THROUGH THE CUMBERSOME PROCESS OF GETTING OUT OF JUMPSEAT (B737). I SHOULD HAVE IMMEDIATELY DONNED MY OXYGEN MASK. FO HAD UNBUCKLED HIS SEAT BELT; TURNED SIDEWAYS AND ALSO WAS WATCHING FAA INSPECTOR. AT THIS POINT INSPECTOR ADVISED ME TO GO ON OXYGEN. I ALSO HAD NOT FLOWN FOR 3 WKS AND FO HAD NOT FLOWN FOR 5 WKS. IT WAS A VERY FAST PACED DAY WITH A LOT OF DISTRS AND A SLIGHTLY RUSTY CREW.