on the fritz

Example: “The heater has been on the fritz since November.”

Origin: American slang, first documented around 1902–03, describing something broken or malfunctioning, and its real origin is genuinely unknown despite one persistently repeated guess. That popular theory credits the newspaper comic strip The Katzenjammer Kids, whose characters Hans and Fritz began appearing right around the same time the phrase entered print — but no actual evidence connects the phrase to the strip, to anyone named Fritz specifically, or to German culture generally. A second theory reaches for pure sound: "fritz" as an onomatopoeic echo of the sputtering noise a failing machine makes. Word researchers who have investigated the phrase in real depth conclude, essentially, that nobody knows, and nobody is likely to find out.