If by "bullying" you mean...

...holding your child accountable for their behavior and lack of participation, then yes, I did that.  The formal complaint to the administrator, by the way was "Mr. Maestro uses his position of authority to bully my child"

I'm not losing sleep over it, although it is hanging on my consciousness more than I would like it to.  Fortunately, the assistant principal has my back on this.  He's even trying to get the kid into another class, which is fine with me because it's is apparent that he never wanted to be in beginning band in the first place. Electives, I believe, should be elected - ultimately that is an issue with counseling and the fact that Former Principal Palpatine axed a chunk of our electives to make way for more honors and AP classes.

The interesting thing about this particular case, however, is the fact that I've been using this student as a sort of guinea-pig for testing out new approaches to difficult students.  Up until a few years ago - this particular mother might have had a point.  I had a bully mode that I could kick into high gear when I wanted to.  The fact that the kids who were on the receiving end of that deserved it is irrelevant - I have re-evaluated and my methods to align with my philosophy as it has evolved over time.  I never liked 'hulking out' on my students.  Rather than establishing authority, it just felt like losing control, and ultimately respect.  At the same time, however, you can't let students walk all over you... so what to do, what to do...

This year (and with this kid in particular) I've adopted an attitude of engaging the student every day in a positive manner, but letting them experience the consequences for their decisions.  As much as possible, I try to handle disciplinary situations privately.  No threats.  No yelling. No intimidation of any kind...  and I've been holding to it.  I feel good about it. 

So, I'm not going to worry too much about this student or his mom...  If I'm lucky, he'll be gone in a little while, anyway.  I also have a student teacher and two trusted TAs who have witnessed my daily struggles with this kid - so that helps.

...ah... but then there's still the presence of his three friends who behave exactly the same way... *sigh*