It's not smart on the individual's part. Has nothing to do with the company. Furthermore, demo tent workers usually aren't really that involved with the company. Some are volunteers even. You can't realistically expect a company to hunt this tent employee down and slap him on the wrist. That tent worker probably won't even care.
Honestly, I think you guys give too much power to such innocuous things. So what if he had a shirt that offends YOU? Why are you letting a shirt bother you to the point of putting a ban on an entire brand based off one tent employee's shirt? You are giving silly shirts and images like the Mervin one power over you.
Great---here we again!