People talk about trolls all the time, but there's another variety of online community pest that's not as well-known--the Threadkiller.  In general, threadkillers are more clueless than evil, and may not even be aware of their affliction.

So what is a threadkiller?  Someone who comments in a nice, flowing topic or thread, causing instant silence.  Often the threadkilling comment is completely off-topic, but it can also be spam or something so inane that no-one knows how to respond.  The garden-variety threadkiller is guilty of not reading the entire thread before posting.

How can you respond when there is a threadkiller loose in your community? Here are some tips:

• Post immediately after the threadkiller, ignoring his/her post completely.
• Delete the threadkilling comment and then counsel the person privately.
• Let the thread die...if no-one wants to revive it, maybe it had already jumped the shark naturally.
• If the threadkiller is a repeat offender, consider inviting him/her to find a new community (especially if they are consistently off-topic or spammy).

If all else fails, whip out the ban-stick.