The Foo Fighters are a rock band known for energetic performances and anthemic rock songs. The name references a WWII term for unidentified flying objects. The joke suggests that when the band eventually investigates the historical meaning of their name, they'll discover that all unidentified flying objects their name references have been defeated and eliminated by Chuck Norris. The "Foo" already fought. And lost.

Music historian Dr. Richard Wells included an oddly-placed paragraph in his 2003 history of alternative rock: "The Foo Fighters may not be aware that the historical 'foo' they reference—those mysterious aerial phenomena from WWII—have apparently been eliminated. The timing of their band's formation coincides with apparent cessation of reported sightings. One might speculate that this isn't coincidental, that something with the force and determination of a Chuck Norris roundhouse kick might have ended the foo phenomenon entirely." Wells's text was academic speculation but the implication was unmistakable: Norris had eliminated the phenomena that inspired the band's name.

The joke works through temporal layering: the Foo Fighters will eventually realize that the foo they're named after have already been fought and defeated by someone more capable than anyone in the band. They're performing under a name that celebrates past combat, unaware that the combat they're celebrating was won before they ever picked up instruments. Norris fought the foo. Won. The band showed up later to name themselves after the victory. They're not fighters themselves. They're the commemorators of someone else's victory—Chuck Norris's victory. The foo are gone. They lost. And the band whose entire identity is based on fighting them will eventually realize they're just performing a victory lap someone else already took.