Seen at Origins 87 : “Terminators : the few, the proud, the machines”.
I have one that says
I thought it was classic when I bought it, but every time I wear it out of the houseI am so sure that I’m gonna get pulled over and have my ass raped with a club. So, it probably wasn’t the wisest purchase I ever made.
LC
“Your boyfriend wants me”
Worn by a guy… 
Old classic; “Shit happens”
Slightly newer version; “Doodoo occurs”
“Peace”
Peace,
mangeorge (Huh?)
Similarly:
“We’re not laughing at you, we’re laughing toward you!”
“Obviously, you have mistaken me for someone who gives a damn”
and:
“Shit Happens” , only printed up-side down! 
My favorite shirt:
“Aren’t I just a f%$@king ray of sunshine?”
Others I like:
“Nobody knows I’m a lesbian” (worn by a guy friend, who is tall, has a shaved head and can look very menacing in a black trenchcoat)
“Don’t make me get my flying monkeys!”
“If you are what you eat, I could be you by morning” (worn by a friend at a horror convention; there’s a picture of him wearing it on my website)
I love t-shirts with cool sayings. I need to buy more.
Sheri
My sister has a t-shirt that says “That’s Ms. Bitch to You!” She also has another one that says “What the f*** are you looking at?” in large letters right across her tits.
A very funny one I saw a few years ago
Wheel of fortune style
**Go F_ck Yo_rself
Would you like to buy a vowel?**
I’ve got one thats the snapple logo except instead on snapple it says snatch. Underneath its got the snapple phrase “best stuff on Earth.” All the guys like it but the girls aren’t necessarily impressed.
One I was thinking of getting my dad for his 60th birthday:
“Men are from Mars, women are from Venus, old farts are from Uranus.”
My favorite shirt is an orange one that says, in black:
Another couple of favorites are:
I got kicked out of school for wearing this f**king t-shirt
If you’re already this close why don’t you just suck my d**k?
from T-Shirt Hell (warning, some offensive shirts/language)
You can make your own at http://www.cafepress.com
I have a t-shirt that says, “If you’re illiterate, you can’t read this,” on the front and, “GO READ A BOOK!” on the back.
I’ve seen camouflage tees that say, “You can’t see me!”
My favorite:
“The Beatings Will Continue Until Morale Improves.”
I got it at a Ren Faire
A mate of mine had a T-Shirt with a picture of Hitler in the Seig Heil Pose, with a caption that read “My hemp plants grew THIS tall last year!”.
I want a T-shirt like Comic Book Guy from The Simpsons: C:\DOS C:\DOS\RUN RUN\DOS\RUN
A fellow I know has a shirt that reads:
As the fates would have it, he happened to be wearing that shirt the very night a grow-house he was visiting was taken down by half a dozen heavily-armed police. They thought it funny enough that they each posed for pictures with him. It’s a funny old world.
My personal favorite is from http://www.theonion.com I think
Your favorite band sucks
Also a truely nerdy one that a friend of mine owns
(on front)
<body>
(on back)
</body>
I thought it was clever. Only fellow nerds would get it…wait I got it…CRAP!
dead0man
“If you think I’m ugly, you should see your mother naked”
Okay I just made it up. But odds are it’s out there somewhere.
If you can read this, you are obviously staring at my tits.
And I have a shirt that says <geek> on the front and </geek> on the back
make that <geek> and </geek>
sorry… I am used to html being stripped out, so I used the markup codes for the brackets. Doh.