>Pretty much all newsgroup readers support twit filters. I think, though, that the name will be something else. Looks like Agent, which I use, calls them "kill filters."

The Sezam ("sesame") BBS has it since 1990. And yes, it still works like that. The syntax is "co[nference] ig[nore] {username} [/d]" where the "/d" switch is to undo the ignore.