In Blur for the Xbox 360, there are a few t-shirts you can unlock for your Xbox 360 avatar to wear.
Friend Rechallenge Avatar T-Shirt – Beat a friends rechallenge
Legend Avatar T-Shirt – Get the first Legend rank in multiplayer
Sticker Avatar T-Shirt – Complete the sticker book
Wreck Avatar T-Shirt – Get the “Been there, got the t-shirt” achievement, by wrecking your first car