On slashdot you could mark people as friends and foes. You could then assign a penalty to posts by foes (and posts by foes of foes and posts of friends of foes,

On slashdot you could mark people as friends and foes. You could then assign a penalty to posts by foes (and posts by foes of foes and posts of friends of foes, I think?) so they were unlikely to meet your 'show post' point threshold and would therefor be hidden.