Bronx cheer (brongks cheer) noun
1. A rude sound indicating disapproval, made by sticking the tongue partly out between the lips and blowing air out in a simulation of flatulence.
2. Any expression of derision or contempt.
[Probably after the Bronx, a borough of New York City, the home of Yankee Stadium, where Yankees fans often expressed their opinion of the umpire's decision or an unfavorable play that way.]
"It wasn't a unanimous Bronx cheer. Many fans stood and applauded for Martinez. Years of excellence outweigh one bad game. Still, it was an out-of-body experience to hear any boos for Pedro on Opening Night at Fenway Park."
-- Dan Shaughnessy; Voices of Fans Are Heard; Boston Globe; Apr 13, 2003.
Bronx cheer has a rather unusual synonym:
raspberry (also razzberry, often shortened to razz).
How in the world could a sound like that come to be known as a raspberry?
To learn this we take a peek at the fascinating working of rhyming slang. "Raspberry tart" was used as a code for "fart" and then the rhyming part was dropped. Other examples of rhyming slang are "butchers" for "look," as in "Take a butchers at this!" (from butcher's hook); "apples" for "stairs" (from apples and pears); china for mate (from china plate). Best-known rhyming slang was used by generations of London Cockneys, but similar rhyming slang is found in many other parts of the world.
Some believe the reference to raspberry is from the appearance of the tongue while "cheering".