Good grief. I'm having trouble buying this whole thing. For one, all the teacher had to do is call you and confirm who the woman was bringing the brownies/treats into the class. Not only that, but I'm sure your son could also tell the teacher who she was, obviously he knows her. And how can the teacher say that they can't serve the brownies because she's a stranger? Obviously the teacher knows that she's picking your son up/dropping him off, allegedly in dirty clothes, so she has to know her. Furthermore, how is this woman getting on the campus or onto school grounds? Doesn't the school check out people before they show up in classrooms? And let's give the school the benefit of the doubt and say they tossed the brownies because they weren't sure of who they were coming from. How do you explain the throwing away of the donuts on your sons birthday? That's just sad, sad, sad. You shouldn't involve your son's teachers in your personal vendetta against your ex. School should be a place where your son can get away from it all. You spend way too much time involving yourself in your ex's affairs. I agree with another poster that we're only getting one very biased side of the story here - something tells me that there's a lot more to it. You need to let it go, and be happy that your son's dad and step-parent are even involved. I'd have been a happy camper when I was a little girl if my step-parent had brought me treats to school on my birthday.
Do we all practice what we preach out there? You have never felt happy when something bad happened to someone bad or someone who had it coming? Sorry but I don't believe that, no one is perfect. And if the biggest flaw I have is being a little happy when the jerk gets it in the end then I can live with that.
The other thing that is getting me is how much everyone is distrusting OP. When in the last few days I have read a couple of other threads where we only had one side of a story and no one jumped on that person. 
