FBI agents say no explosives were found in the shoes of a Qatar diplomat who was subdued by federal air marshals on a United flight to Denver Wednesday night after allegedly telling the marshals, "I'm lighting my shoes on fire."
...A US security official said, "it may have been a massive misunderstanding" and the diplomat's statement may have been a "sarcastic" comment when he was confronted by two air marshals who had been told by flight attendants that smoke was coming from the lavatory.
FBI: No Explosives Found on United Jet in Denver - ABC News