Depends. There is more than one kind, you know. Myself, I’ve mastered the “SBD” so you wouldn’t spell it at all. You’d just smell it. (In case you were wondering, SBD = Silent but Deadly.)
Then there is the little flower – a polite “tooooooooot” in a high pitch that resembles the odeur of skunk cabbage.
Of course, there is the rolling thunderclap – involving the noise of the “verbal raspberry” – pbtpbtpbtpbtpbtpbtpbt