I don't agree that using all-caps "excessively" is a clear violation of Internet custom. All caps is, after all, just another form of italics. People who put entire messages in caps are not only being dumb, they are too lazy to pepper messages with selective caps. The people who drive us crazy are the people who put EVERY MESSAGE in caps.

(Putting a whole message in italics would be just as dumb and rude, but no one ever bothers. For one thing, people who put entire messages in caps probably don't know what italics IS.)