I've wanted clothing in the past that mentioned bass somehow, but nearly all of the sayings I've seen/read before have been too cheesy or self-aggrandizing for me to want to wear in public. The one thing I've found that was perfect was a hat from UglyBassPlayer.com- it had a little round bass clef in the front, and the back just said "Ugly Bass Player." To the point, not cheesy- it was great. I lost mine last year and they don't make them anymore
I'm with Brian here. I've always been a t-shirt guy but as I've entered my 40's, I've grown up a bit

and become more selective in t-shirts.
I'll admit that I've spent a few hours online checking out bass swag only to be disappointed because the shirts are cheezy and way too bold in color and subject matter.
I'll make you a promise that if your wife can make a subtle and tasteful t-shirt, I'll buy one from you.
Let me tell you what
I don't want.
-- I don't want a black or white t-shirt with 10, brightly colored basses, each 10 inches long.
-- I don't want a cheezy saying like the one I used as a college sophomore in my year book picture saying
"Funky bass players finger well"
All these kinds of t-shirts are for kids. They're not refined in any way, especially for a grown up kid such as myself.
Here's what I do want.
-- A softly colored shirt with perhaps a hand drawn "artsy" picture of a bass incorporated along with some swirly lines like the kind you see in the current trend of t-shirts.
-- Forget the catch phrase. However, if you do put one, put it in small writing.
-- I actually like the standard t-shirts manufacturers put out with a hand drawn pic of their bass and the company name. That's cool enough to show your support of a bass builder.
I bought a cool t-shirt from Benevente at the NAMM show back in 2008. They had a nicely drawn bass and their name.
Also, and lastly, (I feel like such a geek writing this whole post), make sure that the t-shirt is a quality shirt and not one of those cheap, dime store quality, shrink to half the size in the wash, crappy kind. It's no fun paying $25 plus dollars for a tee that you never end up wearing.
A year ago, I bought a tee from James Tyler of Tyler guitars in CA off their website. I own and play a Tyler and thought it'd be cool to wear one of their tees. The t-shirt is of very good quality. The design is very cool incorporating more than just a guitar on the t-shirt. You should check them out. Unfortunately, someone at Tyler brilliantly decided to put the print on a bright red t-shirt. Icky and too loud. I'm a 42 year old man. I don't wear bright red t-shirts. The shirt gets occasional wear at sporting events where luckily the home teams wear red.
So, PLEEEEASE make a t-shirt that can be worn by an adult.
Ok, so somebody here has spent a little too much time thinking about this

Guilty as charged!!!