Humourous Bumper Stickers...

[Fetid]

Any short, succinct but cunning one liners?

"Unless you're a haemorrhoid, get off my arse!

[SoCal]

okay, how about:

BE ALERT...WE NEED MORE LERTS
 (My personal favorite)

[Misty]

Dyslexics of the world, untie!

All generalizations are false.

Gravity is a myth.  The Earth SUCKS.

Answer to pick up line:
Sorry, I don't date outside my species.

[Peel]

I think that I think, therefore I think that I am.

[Pissed]

I still miss my ex-wife. But my aim is improving.

[Free 'n Radical]

Quantum Mechanics: The dreams stuff is made of.

[Medico]

He's not dead, he's electroencephalographically challenged.

[trucker]

warning, mine is long

[australia]

we saw these two in Australia a couple of weeks ago

wife and dog missing...reward for dog

you can tell a guy is lying if his lips are moving

[SoSo]

not quite a bumper sticker - but saw "his n hers" T shirts for a biker.
His:
If you can read this - the bitch fell off.

Hers:
I'm the bitch that fell off

[Roy]

Corduroy pillows: They're making headlines!

[Existentialist]

My karma ran over your dogma.

[Legal Physicist]

Gravity- It's not just a good idea, it's the LAW!

[Fat Bob]

Love thy neighbour, but don't get caught

[LevyTea]

All those who believe in psychokinesis raise my hand.