Is it defined where you work? Is it spelled out in detail what you may wear and what you may not?
School is to prepare the students for the real world. The real world does not allow clothing that is offensive or disruptive to the work environment.
If the principal or teacher decides that the clothing is offensive or disruptive, then the clothing is offensive or disruptive. We pay big bucks for their judgment -- let them exercise it.
RP,
Sorry but you are wrong. We do not pay teachers for their 'judgement'. We pay teachers to teach.
If we want to control what the children wear in a work enviroment. Then let's pay them to attend school.
Without school uniforms, the only one who should be able to restrict what a kid wears is the kids parents!