I do not advocate going out looking for trouble but then again the shirt was being sold even without Christians being there to see it.
This will probably end with Christian bashing but I personally feel that this is proof that Christians in the United States have had it too easy for too long. As things get worse and worse many of us may find out what the Lord meant when he said "he that endureth unto the end, the same shall be saved."
I see it as signs of the times he warned us to look for.
May God bless.