If you or somebody else you know is seriously getting stalked, then it may be better to seek assistance outside simply the IRC network.
For information on cyberstalking and how to deal with cyberstalking, take a look at
CyberAngel.org's website. They are an online safety organization that have volunteers and even some law enforcement officers who are trained to deal with these types of situations.
In serious situations, consider talking to your local law enforcement agency.
Regardless of what happens, make sure that you log all incidences with the stalker. The logs should be dated, timestamped and should include the appropropriate contact information - on IRC, a copy of the person's /whois would be appropriate. If the stalking spills over to email and so on, conserve all the headers. You *need* to have a record of the person's IP address.
Report the abuser to their Internet Service Provider.
This site here might offer you a few pointers on how to do that even if it's more oriented for spam reports. In addition,
DALnet's Documentation Website might also be of assistance.
Hope this helps,
Dana