The title of your thread threw me off for a second. Joking about wanting to murder someone is a bit strong for me.
So, I'm glad you are not contemplating murder, or even character assassination.
Anyway, its easy to understand your frustration. The situation needs to be improved and there are things you can do to improve it.
One thing would be to focus on the really important issue(s) and let the less important ones go. The issue of whether your ex sends your son to school in a school shirt vs an approved blue shirt is probably a non-issue. I'd let that go.
The issues that require your action are those having to do with welfare and safety of the child. Shelter, stability, food, rest, support for schoolwork are the priorities. Its also important that you not draw your son in the middle of the parental dispute.
This means that, although you are irate that he was not bathed properly, you should address this to the appropriate channels and powers that can help improve conditions.
Not to your son.
However you have come to this current child custody agreement, it may be time to revise it for a period of 90 days while dad gets more stable. Approach the mediator that helped you two and see if you can get some response this way. It doesn't really matter if dad says you are a mean person, controlling or whatever. That stuff is also in the category of "let it go"....