I don't understand someone sending rude PMs, especially since many people don't clean out their inboxes and those PMs can be around for a long time. A rude reply to a thread is bad enough, but at least those are often buried before too many days. They can be found again, but it takes effort.
I don't get why some people feel the need to be rude in general, anyway, when a person can make the same point politely. Of course sometimes threads escalate into rudeness, but some posters start off with a chip on their shoulders.
Most don't, though, and they are the people that I prefer to deal with.