This is the kind of shirt you buy to demonstrate to people that you have a sense of humor. The kind of man who wears this shirt lives life with a smile on his face, perhaps playing fast and loose with the law until they show up to calm everything down. He probably meant it as a joke, but on this occasion, it's actually happened.
Of all the things you want to be wearing when you have a mugshot taken, this would be fairly close to the bottom of the pile. Whatever he was doing when the police turned up, they obviously didn't consider it to be harmless 'fun and games.' More to the point, the police don't arrest people just for participating in harmless fun and games. The shirt is a lie, and this man needs to re-evaluate his life choices!