"He without sin leave home!"

Why do people wear slogans on their shirts? I might have too bright an imagination, but it honestly disturbs me to read something like "Cash only" on the enormous bosom of some forty-something that looks like a guy. Is it really funny to wear a shirt claiming "I love beer" if it is obvious that you do, I can see that, your huge gut is giving it away. Where is the fuckin joke. I don't get it.