Many people have stopped displaying bumper stickers for the same reason they stopped hitchhiking years ago: The person in the next car might be out to kill you.

Bumper stickers largely fall into five categories: humor ("My Other Car Is . . .") bravado ("Don't Like My Driving?"), affiliation ("Honk If You . . ."), politics ("Free Tibet") and self disclosure ("We're Spending Our Children's Inheritance").

None are safe today with so many people driving around just looking for a reason to lose their temper. It's like making eye contact with an emotionally disturbed person on the street or a yard dog.

Of course there was a day when bumper stickers like "America Love It Or Leave It" and "My Country Right or Wrong" were meant to antagonize. What were people going to do if they disagreed? Get out of their car and shoot you?

Now we know better. That's why the parade of come-and-get-me bumper stickers sported by the twentysomethings in black T-shirts---"Don't Like My Driving? Dial 1-800-Eat ****," "As A Matter A Fact, I Do Own The Road," and "If You Can Read This You?re Too Damn Close"--has disappeared.

So have humorous bumper stickers because someone could take the joke the wrong way:
"I Owe, I Owe, So Off To Work I Go" (At least you have a job, you ingrate!)
"Officer This Is Not An Abandoned Vehicle" (Oh, yeah? I drive the same car!)
"I Support The Right To Arm Bears" (There's nothing funny about threats to the Second Amendment!)
"Why Are You Following Me?" (If I could &^%$ pass you, I would!)

And the "Honk If" stickers that were so popular during CB radio days when no one had cell phones and driving was still a lonely business? "Honk If You Love West Virginia," "Know Jesus," "Believe In Extraterrestrials," "Like To Water Ski"? What if you elicit a stalker instead of a honk buddy?

Of course some bumper stickers, like "Re-defeat Bush," "Made By, Paid For And Driven By An American," and "The Best Man For The Job Is A Woman" are meant to polarize and can earn you instant enemies.

Others like "Our Child Is An Honors Student At Tech High," "I'd Rather Be Snowboarding," and "Commit Random Acts Of Kindness And Senseless Beauty" convey "I'm-better-than-you" in the same way "Baby On Board" famously did 20 years ago. (The latter also obligates you to let people in your lane.)

Others, like "I Brake For Unicorns," "I Brake For Yard Sales" and "Have You Hugged Your Yorkie Today?" annoy people because they're just insipid.

Any bumper sticker on an SUV makes people mad because it magnifies the fact of it being an SUV. Imagine "Are We Having Fun Yet?" "Solar Power!" "My Other Car Is A Skateboard" and "He Who Dies With The Most Toys Wins" on an SUV. That's why SUVs eschew bumper stickers in favor of stuffed animals, flags, yellow ribbons and wreaths on their bumpers at Christmas.

But the truth is, any bumper sticker on any car aggravates people today, from "Mary Kay Cosmetics" and "Pilates" to "We Saw The Wisconsin Dells" and "Hire A Licensed Contractor" because it personalizes the driver. And people are mad to begin with.

They think their running the world from their cells, palms and BlackBerrys but can't even conquer rush-hour traffic. Add the quart of coffee in their system from their Starbucks addiction and no one is exactly humming, "Michael Row the Boat Ashore."

Like hitchhiking or leaving your front door open all night, the days of carefree bumper sticker colloquy and "honk buddies" are over. In fact on today's volatile highways, the only safe stickers are "Support Mental Health Or I'll Kill You" and "I Didn't Take My Meds Today."
Neither one requires a "If You Can Read This You're Too Damn Close" sticker.