This isn't so much a feature request as it is a (possibly) fun suggestion.
A site I used to frequent used to have this system whereby you could anonymously message someone. People used to use it to tell people they liked things, or such. I'm sure some used it to say mean things (which, for some reason, I would expect to happen more often here than there, because, well... DRAMA!), but I never heard of things like that.
A thread was also created whereby people would confess things anonymously to others, who would then post the confession in the thread. It was very interesting at times.