Mahmoud Hussein 18, arrested and jailed in Egypt for 500 days for wearing an anti-torture T-shirt. He is in prison because he wore a T-shirt calling for “a nation without torture” and a scarf celebrating the “25 January Revolution.”.
Thank God we live in a country where this would not happen. We can wear just about anything we want without fear of imprisonment. Of course, even in the US, and other free nations, there are limits if you want to avoid any trouble. For example, the case of Matt Taylor, a scientist working on the Rosetta Project for the European Space Agency. This was the project that landed a vessel on a comet. While being interviewed on television he wore a shirt printed with cartoon drawings of scantily clad women holding guns. There was an uproar from womens groups saying it was offensive and degrading. Ultimately, he tearfully apologized for offending women.
According to Wikipedia, two people have been arrested in the US for wearing offensive t-shirts. However, in both cases the charges were dropped. Some young people have been suspended from school. Their shirts were deemed to be disruptive to the classroom learning environment.
Bottom line, wear what you like, but be aware you may have to apologize later.
And if you are in a foreign country with an oppressive government, be especially careful what you wear.