So, Threadless?
Or maybe, say, Archer* meets *Breaking Bad? 
Too bad this mashup shirt is sold out. Fortunately, you can still find some featuring him with his companion.
I used to have a ton, but now I’m just starting to grow out of the phase I guess. I’m starting to gear more towards band shirts or ones with a logo on it (like Mountain Hardware or Mammut)…
More power to you, though.
Oh no, I’m even lamer than that. I am in an actual dodgeball league, and our league shirts have helped me expand my Grown Ass Woman Who Wears Completely Ridiculous and Childish Tee Shirts collection.
For example, our mascot, to the extent that we have one, is an octopus wearing an exercise headband, while holding a dodgeball in one tentacle, and a beer bottle in the other, which appears on most of our shirts somewhere. Another shirt features a moustachioed taco wearing a foam #1 hand. I have no idea who comes up with these shirts.
Long, long ago, when the earth was young and my three children were very small, I got each of them a baseball jersy with Entropy Elf emblazoned on the chest. One day, years later, the youngest one was wearing the hand-me-down of his oldest brother’s shirt and ONE person got the joke and laughed.
It was worth it.
Between Threadless, TeeFury, Ript, and Woot, I’m probably picking up one to two new nerdy t-shirts a month. My t-shirt collection is now in serious need of pruning. 
See, if you want respect, you need to upgrade that to a heavily armed octopus. (Regrettably, it doesn’t look like that one will be reprinted.)
I’m an engineer at a large corporation, and I wear my geeky t-shirts to the office every day. (Today’s features a red “blood” splat with the slogan “Pass me another character sheet and some better dice.”) They make people smile. If a funny shirt can brighten one person’s day, I’ve made the office a nicer place that day. I generally do dress differently if I’m going to be meeting with a customer representative, but that’s part of the game. Day-to-day, I’m not concerned with meeting some arbitrary “mature” look.
Yeah. I’m thinking I need to start some sort of a rotation at this point so that all of my shirts get some wear–otherwise some wind up buried in the bottom of the drawer. More importantly, they don’t all fit in the drawer any more. Perhaps monthly sets of 10, with a nice mix of geeky, clever/whimsical/whatever, and Gogol Bordello (because that’s really the only rock t-shirts I have).
Redbubble.
Wow. I just checked out RedBubble. Those are some really cool shirts. But, 25 bucks for one shirt? I can only go so far for my geeky interests.
T-shirtgasm today–all of my shirts came in at once! Wearing the Dunwall one now. 
I think I have posted this here before: this is my favourite geeky shirt. I get a lot of blank stares though, so far only one person got the joke.
I also like wearing this dress. It makes people smile at me a lot. 
Those are both pretty awesome.
I’d get in trouble for trying to turn one of your pieces…
But only if I run towards you. If I run away, it will turn infra-red.
I made up a sweatshirt with the legend The Witch of Agnesi Project, with a construction of the mathematical device The Witch of Agnesi, subtly altered to look like the “hanged man” stick figure from The Blair Witch Project. I even made the typeface identical to the movie poster from The Blair Witch Project.
No one has yet “gotten” this shirt. I’ve worn it to science fiction conventions, comic book stores, MIT, and gatherings of Geeks. It’s hopeless
Maybe I would’ve gotten more positive results with this:
You’re right, of course. But at that speed running backwards (or turning your head around) would be pretty dangerous. 
…especially if you’re holding scissors.
Can’t beat Mac pride + hipsterism!