Sound used to imitate a mentally retarded person as an answer to an obvious remark or question. The person using "duh" is thereby sarcastically indicating that he/she is not retarded and the forgoing remark or question is obvious to him/her.
Him: Hey, to insert a column you have to press the column insert menu!
Me: Duh! No kidding!
Nonexistent german-sounding word for sperm or semen derived from the english word "spunk". Sascha Baron Cohen introduced this word to corroborate the austrian (hence german-speaking) roots of his alias Brüno.