@engineer,
There are several problems with your suggestion Engineer. You are ignoring the nature of adolescence and of education; how does what you suggest prepare students for the working world where there will be standards?
But let me focus on the idea of community. The inability to understand community is a big reason that for all the media time that progressive ideas yet, they fail to get very much traction politically. You are basically sitting where your educated white Collar job puts you, and dictating policies for any general educational setting in any local community.
It is interesting that most progressives will draw a line (you seem to an exception). I already posted the excerpt from the Cambridge MA Student Handbook (an exceeding liberal public school district) that is willing to draw a line about what is offensive that includes "bare midriffs".
What is wrong with letting these local school districts deal with these issues according to their community standards? What we have is a national political movement using the national press.
People who violate some moral philosophy set by educated White people in the upper-middle class suburbs of Blue states are publicly shamed in the national press. This is part of the reason that Democrats lose elections.
Is this really a good thing?
You ask who defines what is inappropriate? I think that should be the local community. There is a subjective line that needs to be drawn by each local community... and each community will be different. Enforcing some homogeneous standard through national shaming in the press and social media somehow seems unhelpful.