I'm not saying, Big Mick, that it isn't fair enough to comment sometimes on something an un-named GUEST has posted, especially when other people are drawn in. But I think it is generally a mistake to address the poster directly.

And it's always to remember that "this person" might not be the same this time as "this person" last time. A nameless GUEST, by definition, excludes themselves as being treated as "this person", or as a serious contributor to any discussion, since pretty clearly that's not his or her priority.