I remember when I was in high school, and I wanted to make my own shirt, I went and bought iron-on letters at Wal-Mart and did it myself.
Bang-On gives kids today another opportunity to be lazy, with pre-made t-shirt designs that you can "customize", or you can actually get creative and do something original. Exactly the same kind of deal as a lot of other stores around, particularly Exile in Kensington, but just a central location on a touristy strip of town.
I'm pretty sure this place is a chain, because I think I've seen a location in Ottawa and possibly Montreal. And the Toronto location isn't bad, I'm just bitter that my high school efforts can now be accomplished so easily. Sigh.
If you want to make a funny t-shirt, come here to do it. They also have racks of fun sunglasses and belt buckles, good gifts if you are gifting for the ever-fickle teenager.