the sound emitted when farting

Adj. Something that is expected to have a long lifespan by virtue of having existed for a long time, based on the lindy effect, named for the New York restaurant Lindy's, coined by Albert Goldman and popularized by Nassim Taleb.

PFFFT!! PFFFT The sound your lips pressed together and blowing air through them makes as you witness some idiot make a bigger fool of him or herself either by what they said, wrote, did. A show of utter disgust, no fear and the act of totally brushing someone off by dismissing them as a complete moron not worthy of one's time.

note: could be immediately followed by a brushing away with one's hand ending with a palm towards the buffoon.

The sound you make when someone says somthing really stupid.

The sound you make when someone says something that you don't like, want to forget, or disagree with.

When somone says something really, really stupid and useless, A sound made to wind people up.
The Winner of all arguments.

disbelief. doubt.