One story originally told by Martin Caidin in his book on the P38, was the tale of the phantom P38, one that had been captured by the Italians and was flown in US colors by one of their pilots, Guido Rossi, to shoot down stragglers after coming in close under the guise of being an escort.
Supposedly, this morphed into a struggle between Rossi and one of his victims, Lt Harold Fischer, who survived the shoot down. Fischer requested a YB40, a B17 with a lot of extra guns and ammunition, to go hunting Rossi. Fischer went so far as to find Rossi's wife, who was living in Allied controlled territory, and paint her picture and name on the YB40 to draw Rossi in, and eventually shoot him down. Both survived the war. When Fischer died as the result of a crash during the Berlin airlift, Rossi was at his funeral.
The way the story is told has elements of 1940's fiction about it, so it may have 'grown in the telling'. But, like a lot of wartime stories, it probably derives from an actual incident.
Interesting side story that came up while looking into this... the 500 round belts of ammunition for the M2 50 caliber machine guns on the B17 and B24 were 27 feet long. Supposedly, the expression 'give them the whole nine yards' derived from a bomber gunner dumping an entire belt of ammunition at an attacker.