Mmphfff
Mmphfff. It comes out spontaneously. I catch myself making that sound again, like I've really turned into a crotchety old Jewish woman who says, "oh vey" as her bones creak when she sits, or Cher's mom, Olympia Dukakis in Moonstruck, who sighs, "hahhh" like she's on her deathbed because men chase other women.
I can't regulate it, and I don't recall the first time I heard it come from my body. But there it is when the teens can't figure out how to turn on the water for the industrial sink, even though I've shown them 457 times, "Mmphfff." Or when someone writes an amount 180$ because maybe they are not teaching U.S. currency notation in schools anymore? "Mmphfff" Or when I have to say, "Good Morning," to them while I grit my teeth and fake smile until I can get into my car and slam the door, "Mmphfff."
A consonant or two away and it would be, "mmm," tasty, or "hmm," ponderous, or "humph" as I'm thinking "f*** in polite company. But "mmphfff" comes out whether I'm alone or with others – it doesn't discriminate. Sometimes it's got a snide smirk of condescension, like the French, who purse their lips and let out a "pfhuu," at ugly Americans who can't speak French. Maybe it's a unique amalgam of my upbringing and collective consciousness.
All I know is that it's my signature of exasperation and world-weariness. If you've got your own, you know!