The ACLU became involved in a case in California when a student had the US flag on her back pack (or clothing). The school had barred her from attending classes unless she removed the flag. The school reversed that decision when the ACLU threatened to take the school district to court for violating her First Amendment rights.What if you watch your neighbors fly Islamic State flags on their homes, apartment windows or display them on their cars, aren't they protected by their US Constitutional First amendment to freedom of speech?
Could they be arrested even though they have their rights?
The Constitution trumps school decisions, local and state laws, and personal opinion about what is appropriate and what isn't.