hmmpff (Nearly infinite variations of this spelling involving more M's and/or F's.)
harumpff (spelling may vary)
Worker: "Hmmmpff." (tone of indifference)
"I thought that after tipping the homeless guy $20, the directions he gave us would have been in the RIGHT direction...hmmmpff." (tone of confusion)
Bert: "Kenny G is both a brilliant musician and a sex icon."
Mike: "Hmmmpff." (almost any tone, such as shock, disinterest, inquisitive, etc)