SITTING in the back of a taxi as it slowed down at a toll plaza on the way into Manhattan from La Guardia airport on Monday, I was startled to hear a string of obscenities directed at the taxi-driver from the open window of a van driving alongside.
"Learn to drive, you mother f...er! Get off the road. Get outta here! Go back to Africa!" the van-driver shouted. The invective continued every time he came level as the lanes of traffic edged forward.
My Ethiopian taxi-driver's offence apparently was to edge cheekily in front of the van when changing lanes, something which happens all the time in American city streets.
The nasty van-driver eventually drove off, and nothing came of it. But these things can get out of hand. Two drivers got so mad at each other in New York recently that one shot the other dead and is now sitting in prison rather than behind a wheel.
Even in the balmier driving climate of Washington, roadway rudeness is becoming more common and lethal.
On Wednesday, a driver began screaming and giving finger signs at another on the George Washington Parkway. One was called Narkey Terry (I'm not making his name up). He raced his Jeep Cherokee against the 26-year-old driver of a Chevrolet Beretta on the northbound lane, according to witnesses. Both lost control, crossed the median and smashed into two other cars, killing three people. Narkey survived. His competitor didn't.
The growing problem of rudeness on the roads is worrying Maryland state police, who have been trying to curb it with Operation Aggressive Driver, aimed at warning off "tail-gaters" and other road hogs.
A survey by the Potomac division of the American Automobile Association showed that four out of 10 drivers believe aggressive behaviour to be the biggest problem on the roads, more than drunken driving.
"11 has been said that the most dangerous drug on the highway is testosterone," Charles Hurley of the Arlington Insurance Institute for Highway Safety, told a Washington newspaper.
But is the rise of rudeness just a motoring phenomenon? William Jeannes, publisher of Car and Driver Magazine, doesn't think so.
"I think there's more rudeness and aggression everywhere. It is something I find very depressing about our country, he was quoted as saying this week.
A survey carried out by US News and World Report in February bears him out. It concluded that most Americans feel that the country has hit an all-time low in manners, and is evidence of a profound social breakdown.
In the land of "Have a nice day" nine out of 10 people consider incivility a serious problem, and more than three-quarters think the problem has worsened in the last 10 years. In-your-face nastiness has become part of a rising tide of social crudity.
It can be found everywhere.
In politics candidates trash their opponent's character in negative advertising. Some 73 per cent of Americans blame mean-spirited campaigns for making people less civil.
On television, programmes like Crossfire on CNN encourage politicians and pundits to shout each other down. Soap operas compete with freak programmes where, typically, a runaway transvestite teenager yells abuse at a mother who has dumped his abusive father for a lesbian lover.
Bill Maher, host of a popular show called Politically Incorrect characterised such shows as a daily monument to the breakdown of civilisation. "I call theme gawk shows," he said recently. "What's uncivil to me is this idea that the worst thing you could be is not famous.
But for excellence in rudeness, radio talk shows are on a par with New York van-drivers. More than half of Americans blame them for the growing coarseness in public discourse.
One talk show host on WABC in New York, Bob Grant, who has called welfare mothers "maggots" and black criminals" sub-human scum on the air, reached a new low as the nation's foul-mouth this month.
In the early hours after the plane carrying the Commerce Secretary, Mr Ron Brown, crashed in Croatia, he announced that he was sure Mr Brown had survived "because at heart I'm a pessimist".
But even talk radio incivility has its limits. In a small victory over nastiness, the radio station terminated Grant this week.
Have a nice day. Hey! I'm talking to you.