https://en.wiktionary.org/wiki/der
Sep 21, 2022 · (Australia) Disdainful indication that something is obvious.· (Australia) Indication of stupidity. 1979, Gabrielle Carey and Kathy Lette, Puberty Blues, page 46: `Sprung!' cried Jeff Basin, the local dubbo. 'Oh, der,' moaned Boardie sarcastically.··Nonstandard spelling of there.