“My karma ran over my dogma”
“Don’t tell my mother I’m a lawyer, she thinks I’m a crack-dealing pimp”, seen on the (very expensive) vehicle of a local barrister.
When I saw a girl (who was 'bout 20, trashy-slutty-yet sexy) who had a sticker that said “Mean People Suck, but I Swallow” I almost drove off the road.
Also, there’s a dump truck company in this area that lets the drivers personalize their trucks by having messages painted on the back of the trucks. Most have goofy little sayings, but the one I liked the best was “Be a Flirt, Lift your Shirt.” I don’t know if he gets flashed, but I suppose it is worth a shot.
In the unique and perplexing vein, my brother has a custom made window sticker on his car that says:
“cheesephonedesk handtablemagazine ducktapedtarp brokechair cakecase forkinthehead beanskintreetwig”
I still don’t know if it means anything, though he claims that there’s a story behind it.
Jesus Saves
but Buddha recycles
I’ve seen two variants of this:
[li] Who pee’d in your gene pool?[/li][li] You’re from the shallow end of the gene pool, aren’t you?[/li]
My favs:
Hi! I’m the Dread Pirate Roberts[sup]TM[/sup] #7326. Ask me about franchise opportunities!
[paraphrase - I can’t remember it correctly, but damned near drove off the rode when I saw it]
Red meat isn’t bad for you. Fuzzy green meat is bad for you.
and on my car - Born-again Reincarnationist
A friend of mine tells me he’s seen one that says:
No, You Suck
signed: The Mean People
I like it. Too bad I haven’t seen it myself.
There is a car driving around here in Sprinfield, Illinois with very darkly tinted windows and hopped up wheels. In the back window is a sticker that says, “Don’t laugh - your daughter may be in here.”
Yikes!
Tibs.
“when you invite people to think your are inviting revolution.”
I have the best bumpersticker EVER (IMHO,anyway)
It has the head od The Tick, and says:
Honk if you love justice!
How cool is that?
Written in the dirt on the back of a truck
“I wish my wife was this dirty” 
Me! Me!
“Vegetarians do it with relish…and carry a condiment!”
On the same car:
“Kill Your Television”
Bart Simpson saying “Yo, Dude!”
Seen on the back of a motorcycle jacket:
“If you can read this, the bitch fell off.”
I saw a variation of this:
“Guns don’t kill people. Radical Pro-Lifers kill people.”
I love this one:
Jesus loves you, the rest of us think you’re an asshole!
Seeing as I absolutely can’t stand people that drive while on the cell phone, I have this on my car
Maybe you would drive better with that cell phone shoved up your ass!
“Get any closer and I’ll EAT you.”
“Don’t piss me off. I’m running out of places to hide the dead bodies.”
“QQQQ”
“I <spade> my dog.”
“Horn broken. Watch for finger.”
And of course, many of the ones that have already been mentioned.
Have one on mine, under the “Best4x4xfar” sticker, I thought the following was rather apt considering my Rangie was built before that certain German firm came in and Asset Striped - I mean, ran the Rover Group
100% BMW Free
but have seen these on the back of other Land Rovers:
“You are My Crumple Zone”
“For the last time, its not a f**king Jeep”
I found these amusing.
Keep honking. I’m reloading.
He who lives by the sword dies by the crossbow bolt.
Blood is thicker than water and much tastier.
However, this one was so superior sounding it bugged me.
At a friends school, all children are honored.
I like mine “I like your girlfriend” and I used to have one that said “life is short, party naked” with calvin running naked on it.
I was nearly run off of a two-lane undivided highway by a tractor-trailer with a bumper sticker on the back of the trailer that read:
“If you can’t run with the big dogs, stay on the porch.”