Wow! I think we've lost touch with reality here...this is not about PTO regulations being followed. It's about bad behavior.
Bad behaviour in real life (for adults, kids, pets, ad nauseum) has consequences. If you really want this to be a lesson for your child, take your deserved lumps. Have the kids had to take any responsability for their mean behavior to one another?
Once you enter the 'out of control' zone you kind of lose the opportunity to have a say in your consequences, and are at the mercy of those in authority (or majority in this case). The yelling parents put the rest of the board in a very bad position. If no precedent stands in your group, then you have no right to question their decision or manner of reaching said decision under the duress that you caused. Just the fact that you slept so well seems to indicate that you are oblivious to how your behaviour affects those around you.
You did the right thing in apologizing and making up with the other parents (Mom, Dad and child I hope). But if you are justifying your words, but not the yelling of them, then you are justifying your anger. I don't think anger is ever constructive, even if you think the other person 'deserved' it. This has turned into a 'mean (grown up) girls' episode, when it should have been dealt with as an episode with the 'mean' kids privately. You are first, foremost and directly responsible for raising your own child. No PTO business is more important that parenting, especially if your kid is being mean, destructive, obnoxious, or disrespectful (all of ours can be this at times, and boy can they pick their moments!). This calls for immediate parental intervention and some sort of negative consequence for the kid...not the parents!
As far as the 'mule/workload' issue, at least they think enough of you to extend opportunities for you (and your child) to interact and enjoy PTO activities. It is a priveledge to be welcomed into the school (some principals don't welcome any parent involvement) and especially back into a group where you've showed your heiny. If you enjoyed your activities, then there's no real reason to stop doing them just because you lost the priveledge and trust of a leadership position. If your child has household chores, and a priveledge....lets say they're going to get to go to the movies, and their behaviour causes them to lose their priveledge (which they should have no say in), do you still expect them to be a part of the household team and do her 'chores'? Of course! She's still part of the team/family. As an adult, you have the opportunity here to choose your own chores. Let's not pout. It's your committment to the kids (all the kids) and the school that got you into this. If you're still committed, then keep on going. It will take a big dose of humility to go about it with the right attitude.
I might volunteer to do the babysitting a few nights at the meetings so that I could keep an eye on my kids interaction and friendship skills. This would say a lot about your character, and show your child that you mean business...and oh, how you should mean business with bullying behaviour.
If you ever do regain your position of president in time, keep a sense of humor...add a bad behavior removal clause as the first order of business.

Just to clarify your position.