Slow pass is pretty common in NC, SC, and GA in my experience. There is always some ignorant nut. It has gotten to the point that no VHF communication is necessary. When the considerate fast boat hits my wake he backs off and I drop to idle speed. Either we both know the drill or we don't, but when we both do it works very well. The way I see it, it is the choice of the passer whether to be considerate or not. But by slowing down, it is also considerate to the passer as well, and makes it easier for them....
The slow pass came up in a thread here not too long ago and one of the regulars (with a claim of many years boating experience) stated that he would not slow down for a slow pass.
You never know who is thinking what, but I've learned that it's a waste of time and effort to try to control or change other people's behavior when you don't have the authority to do so.