Along the same lines if you where designer tee shirts French Connection UK in Disney World Florida people are asked to either change or turn them inside out by the cast members. They don't cause offence to me but the Americans have a different opinion.
I can't see how it could offend anyone, are we not getting a bit too PC. I think its quite funny. I've got a couple of t shirts that I wear with writing on them, no swearing admitadly but the word on the guys t shirt wasn't swearing either.
If he was wearing a t shirt that offended black people or whatever I could see the point but I personally think its funny and think its a storm in a t cup. You know the wording I mean, if it used that language then yes it would be offensive but this one isn't.
I've seen lots of these type of "T" shirt and to me they are all offensive. They certainly should not be worn in public. By the way I am no prude, I served 23 years in the forces. But it just shows to me the level some members of the public have lowered themselves to.