Green’s Dictionary of Slang

gradoo! excl.

[according to Eble, Campus Slang, 2 Nov. 1973: ‘literally bird faeces’, although in what language is not stated]

(US campus) an excl. of frustration or disgust.

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[US]Eble Campus Sl. Nov. 2: gradoo [...] (literally bird faeces) : Gradoo, when is he ever going to grow up.