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1.
An indignifying response to a ridiculous joke, comment or remark; usually indicating a hint of sarcasm or speechlessness; usually pronounced with a deep pitch in one's voice, reminiscent of a walrus.

Pronunciation : Oh-hu
"I busted your girlfriend making out with an octopus, and she said it was the best sex she ever had."
"Uh-hu!"
by Burak Haliloglu April 16, 2006
 
2.
anytime someone is busting your balls or is annoying, its the simple monotone answer.
randome guy: "hey bob, ur a dick-head"

bob: "uhhu"
by warrick April 01, 2004