The line comes from the German dub of Wie Pech und Schwefel, the 1974 Bud Spencer and Terence Hill comedy known in English as Watch Out, We're Mad. The duo's dubbed films became cult favourites in Germany, where their brawling humour and inventive insults were hugely popular. This particular insult survived because its sparrow-and-kneecap comparison is so oddly specific that it still sounds funny out of context. Shared on soundboards and in meme edits, it is now used far beyond the film as a quick German-language roast.