Was just thinking over some of the funny T-shirts I've seen in my life. Here are a few:
Large, close up head-shot of a rooster. Underneath, a caption saying "CHICKEN SHIRT".
A couple on the beach, the wife very pregnant. Her t-shirt: an arrow pointing to her tummy and a sign saying, "Under Construction". His t-shirt: "Construction Worker".
My personal favorite: a plain shirt with no logo or picture of any kind saying in plain print: "I am the man from Nantucket".