Just my two cents worth:

The relationship between performer and audience goes two ways. Most self respecting performers want a certain level of respect from their audience. While some like more banter and give-and-take than others, I cannot imagine very many performers that would like some jerk in the audience to start playing a kazoo in the middle of a song.

It goes both ways. The audience does not want to be insulted by anything the performer does. If you do not like a song you can leave. If you don't like the clothing you can also leave. I would consider such a t-shirt as beyond vulgar and I would immediately leave. Clinton, a t-shirt is not just a t-shirt. What you wear reflects what you think. Shirts with obscenities and vulgar statements let me know that the performer is probably someone I want to stay away from. That might be an innacurate first impression, but as the saying goes, you only have one chance.

To me, if you want the audience to listen to the music, to evaluate the words of your songs, and to share in your talent, just wear clothing with no statements of any kind, and let the music do the magic. In my opinion, anyone who has to result to vulgarity (spoken, sung or worn) is a very, very, poor communicator.

Freightdawg