I think it takes multiple flags to flag kill a comment, but you can also vouch for them (I do this regularly). Click on the timestamp next to the comment and yo

I think it takes multiple flags to flag kill a comment, but you can also vouch for them (I do this regularly). Click on the timestamp next to the comment and you'll get a vouch option. I think this takes a karma threshold, probably the same one as downvoting (500 or so).