The guy wore the shirt to a celebration after working with those co-workers for 10 years. It wasn't intended to look "professional" and I'm pretty sure none of those co-workers were offended. The reason the shirt was a bad idea is that it was easily misinterpreted by people watching the press conference.
Edit2: I agree with bunnymancer's comment as far as it goes. But I don't think the shirt is a very big problem. It would be almost insignificant if it weren't interacting with the big problem we already have.
Edit: I didn't see it at the time, but this article exactly reflects my perspective on the thing. http://www.theatlantic.com/politics/archive/2014/11/why-a-sh...
Edit2: I agree with bunnymancer's comment as far as it goes. But I don't think the shirt is a very big problem. It would be almost insignificant if it weren't interacting with the big problem we already have.