Have you ever projected a flashlight into an approaching fog bank? Or seen search lights play on the clouds? I’ve often thought that the foo-fighter phenomenon sounds suspiciously like a light source from the aircraft being directed onto its own contrail. That would explain why you couldn’t get away from it.
Tail gunners in bombers had a lot of time on their hands, were isolated from the rest of the crew, and their own bodies would block any reflection back down the gunner tube. Some of them, no doubt, appreciated a good practical joke now and then. However, that explanation has to my knowledge never been admitted by anyone, and only explains one small subset of the sightings.