When I see this on the tag of a t-shirt I laugh so hard. Everybody knows that t-shirts shrink. I’ve purchased t-shirts and worn them once only to find them shrinking after they go through the wash and dryer. Then they don’t fit right.
My suggestion: The first 5 times you wash a new t-shirt DON’T put it in the dryer. Instead, hang it on a hanger and let it dry. The heat causes the t-shirt to shrink. See this Google Answers article for some extra tips and information. And this guide: How to Buy T-Shirts.