Various ones I can remember:
"Vegetarian: Primitive Word For Lousy Hunter"
"If You Can Read This, I've Lost My Trailer."
"Learn from your parents' mistakes - use birth control"
"Don't Be Sexist - Broads Hate That" (on a car that I used to work on at the dealership - I'll never forget it.)
"Honk If You Slept With Clinton"
"I killed a 6-pack just to watch it die"
"Your kid may be an honors student, but you're still an idiot" (see lots of those around here)
Seen at some computer conventions...Defcon anyone?
"We are Microsoft. Resistance Is Futile. You Will Be Assimilated"
"It said 'Insert disk #3', but only two will fit"
"The name is Baud, James Baud"
"Programmer - a red-eyed, mumbling mammal capable of conversing with inanimate objects"
"I brake for LAN parties"
"There's no place like 127.0.0.1"
"geek."
"No I will not fix your computer."
"fsck -y" (that's actually a unix command)
