No it's not THEIR problem, it's the schools problem because they have to address any bullying and keep the kid safe. The easiest way to deal with that is to have the kid not carry the purse.
I also don't understand where people get the idea that just anything should be allowed. As adults that's not true. If you have an office job you don't show up for work in a bikini, you were a suit. If you work at McDonalds you were the company uniform. School is to prepare children for the adult world and the adult world has expectations of certain dress that is proper for the job. This is why schools public and private should have uniforms and dress codes. Work and school is not where you make self expression,it's where you make corporate expression. If you want to express yourself in a unusual way than I'm sure your boss would tell you to do it on your own time. This kid should do it on his own time outside of school.
As for the biker thing,not everybody has a group of bikers to protect their kid.
The boy would be able to take his floral bag to work at McDonalds, and leave it in his locker of staff room.
Office worker, he could probably do the same thing.
Female office workers used to be able to wear a bikini to the office Christmas party and show off their newly acquired gym skills by doing tumbles on a mat along the floor.
If he were an 'eccentric lawyer' he could also probably be allowed to take the bag to the office, to court, or anywhere he liked.
I was once in a barrister's office, he had a skull atop his robe/coat stand.
This kid has legal rights, which the school should be protecting.
Casey, an overweight boy, was being bullied at school.
He complained to the teachers...60 or so times in writing.
The teachers and principal did nothing.
One day Casey fought back;
[ame=http://www.youtube.com/watch?v=isfn4OxCPQs]Victim Fights Back In NSW Sydney School | 'Casey' - YouTube[/ame]