Re: Barbecue etiquette
This is one of those situations where you can move, deal with it and/or tell him about it. I hope it's safe to assume that the guy was not doing anything on purpose, other than cooking some BBQ.
Don't go sweeping your deck as you go by in hopes that he can put 2 and 2 together. That's pretty much passive aggressive. If you want to let him know what happened, just tell him. If someone told me this happened to them while I was BBQing, I would think twice about neighboring boats and be more careful.
The comment about letting go of the holding tank is ridiculous. Don't ever do that.
It doesn't make any difference who anchors first. There are no dibs on anchoring spots and surrounding waters. Anchor a safe distance away and you are as equal as the next guy.