Sentences that begin this way usually tell you more about the community manager than the member.
I have this one member that's always antagonizing everyone else.
I have this one member that's hyperactive. S/he posts on every single comment/thread.
I have this one member member that's always criticizing us.
Why does this tell you a lot about the community manager?
1) They're focused on the negative. This happens a lot. A community manager becomes overly focused on the impossible task of making single members change their behaviour rather than keeping their happy members happy.
2) They haven't resolved the problem yet. This is most surprising. A community manager complains about a problem they don't have a process for resolving.
3) They don't know if this is a problem. If a member is a problem, there should be data to support it.
Are the antagonized members leaving in droves? Are you receiving regular complaints? Is the hyperactive member reducing the contributions of other members? Is their response the final one or are they stimulating further contributions from other members? What does your data say? Does the critical member have a point or a grudge? Are you resolving the issue or removing the member? Are they provoking more criticism from others?
The things that annoy you could be very different from the things that matter to the majority of members in your community.