My educated guess on this topic leads me to the age-old practice of back-stabbing.
Why is it exactly, that people feel the need to say nasty, untrue things about other human beings? Especially those who hardly know the party in question?
I suppose to each his own is the explanatory phrase for this one, but I for one, do not make a point of being rude to someone in secret.
I mean, let's be serious for a moment. Who are you to splatter someones character, when you're too ashamed to admit to your own identity?
Interesting, but I always thought that those who spoke openly were remembered, and those who remained anonymous were never noticed in the first place...