A meme that orignates as a witty phrase/theme printed on graphic tee's found in stores, and can sometimes seep over onto the internets. Can be created by large corporations, or anyone on a "create your own shirt" site, like cafepress.
A true shirt meme is first seen on a shirt - however memes can sometimes
jump from the internet to the real
world by making appearances on custom tee shirts, or on shirts where a big clothing corporation catches onto the trend, and exploits it, bringing it into the
mainstream.
Has contributed to the 'merchandising' of memes, and the spread of memes
outside the bounds of the internet. example is the ability to purchase a mug with Urban definitions on it.