It should be memorable, provocative, and concise.
I was thinking:
KINDER, GENTLER MACHINE GUN HAND
or
HAPPINESS IS A WARM GUN
It need not be pistol themed. If you had a bunch of iron-on letters on hand, what would you choose? The more esoteric, the worse as far as I’m concerned.
From Elvis Costello’s I’m not Angry
There’s No Such Thing as an Original Sin
Dunno why, but I always thought that sounded neat.
“Where’s that confounded bridge?”
“I got a woman, wanna ball all day.”
or
“That’s great, it starts with an earthquake…”
I Work Myself To Death Just To Fit In
I had a baseball shirt as a teenager that said “Living is easy with eyes closed” on the front, and “Strawberry” on the back.
I don’t know how old you are, but you could try either
“I hope I die before I get old”
or
“Too old to rock and roll, too young to die”
The papers want to know whose shirt you wear.
Sadness is my luxury. That’s my most recent fave.
I just had this thought yesterday, while listening to Tom Waits’ ‘Step Right Up’
I really wanted to make a tee shirt saying in large letters:
“The Large Print Giveth, and the Small Print Taketh Away”
And underneath that in small print, most of the lyrics of the song.
I’d buy that for a moderate sum.
Tim
WILCO!
My first thought was “I dreamed about killing you again last night, and it felt alright to me.”
And don’t forget
To give me back this T-shirt
What’s so funny 'bout peace, love and understanding?
Some from Warren Zevon:
I’ll sleep when I’m dead.
If California slides into the ocean, like the mystics and statistics say it will, I predict this motel will be standing until I pay my bill.
Sweet Home Alabama, play that dead band’s song. Turn those speakers up full blast; play it all night long.
Send lawyers, guns and money. The shit has hit the fan.
The point of departure is not to return
It would be cool to just do images of Lawyers, Guns and Money to find other Zevon fans, but the lawyer part might be tricky.
Lionel Hutz.
Maybe Saul Goodman.
I like that. I would wear one of those. 
Theme from Squidbillies!
My dreams are all dead and buried…
Imagine no religion
I know it’s only rock and roll,
But I like it
Lazing on this sunny afternoon
Be cool or be cast out
Get back to where you once belonged
(There’s a million of them I could think of…given time.)