My then-teenage brother once went through US immigration wearing a t-shirt branded with the initials of the then-popular brand, French Connection UK.

Needless to say the US immigration officials took some offense and asked him a bunch of questions. I'm not sure they realised it didn't say what they thought it did, even after we explained about French Connection.

These were obviously simpler times as I also as a teenager once went through US immigration wearing a Threadless Community Party t-shirt: https://www.threadless.com/product/383/the_communist_party

A friend of mine got pulled aside for extra questioning at Newark in the mid-90s because he was wearing a t-shirt that proclaimed "Smoke me a kipper, I'll be back for breakfast". I think the officer presumed it was some sort of drug reference.

I'm not going to tell you what you can and can't do. But a quick google should show you how wise that is. Or rather, isn't:

https://www.google.com/search?q=airport+offensive+tshirt

Probably don't wear a shirt with blinking lights on it either.

http://boingboing.net/2007/09/21/mit-student-arrested.html