Doh

Doh!

(Source)

Homer Simpson may have made this grunt famous, but it is actually first attested in 1945 in a BBC radio script for a program called It's That Man Again. A similar interjection was used by character actor James Finlayson in Laurel and Hardy films, which was the inspiration for Dan Castellaneta's interpretation of "annoyed grunt" in The Simpsons scripts.