I’d love to see the OP defend his right to wear said shirt to work. (Which at this point I could definitely see happening)
I can really see why you would want that tee shirt back.
Look at it as the fashion police doing you a favour.
And spelling, and sentence structure and so on. You’ll get a lot farther in life (and be able to get a job that will allow you to by all the nasty ugly tees you want), if you spent your time in school learning English and the other basics, rather than fighting over what does, or does not constitute art.
As for your shirt. 1st step, negotiate with your MOTHER (since she told the principal not to give you the shirt), to get it, take it back to the store, and get your money back. Frankly though, If my 18 year old son bought and wore a shirt like that, I’d do the same thing your mom did.
Your “rights” end where others’ eyes in public begin. You don’t have a right to pollute my viewing space.