Hi Glock,
I sure hope that’s not your real name. I think it is great that you are bold about standing up for your faith in public. But for Sunday Mass I would hope that you wear something better than a tee-shirt. If you were meeting the President of the United States or the Governor of your state formally, you would wear your best clothes. At Sunday Mass you are formally acknowledging God in a public way. Only the best for Him!
Also, wearing anything with writing on it to Mass can be distracting from what is most important there, i.e, acknowledging His passion and death.
Fr. Vincent Serpa, O.P.