This is one of my all time favs.
Woot! pioneered the whole “one day, one deal” idea. Now they’ve expanded by launching shirt.woot! – one shirt, every day. Seen a few very good ones on there so far.
Oh damn, I’m in trouble. Or, I should say, my bank account is in trouble.
They don’t ship internationally 
I love threadless. My daughter has about 20 shirts from there, none of which are still available to link to, sadly. My favorites are “The Fast Supper” which is a parody of The Last Supper featuring Ronald McDonald, Wendy, the Burger King, and several other mascots I can’t remember, although I think one of them was the Arby’s oven mitt, and another of a kid riding on a zombie’s back, using the brain-and-stick method of forward propulsion.
I have a homemade shirt (a gift from a friend) that says “sex: it’s my anti-drug”. I once made a congratulatory shirt for a friend who won an honor at law school: “Best Oralist”. 
And I love this shirt so much I bought it AGAIN when the first one got too big.
Also, I like all the ones on Scary Go Round.
Even more fine shirts! Lib: I like the concept, but oh, the AWFUL design.
I have a Neighborhoodie. It’s amazingly comfy and cozy. Asphalt gray with bling bling gold letters in the Boston font. It says “Brookside” and I added a few rhinestones.
My favorite t-shirt is this one with a beautiful dead fish on it. No clever sayings, though.