Some people come on IRC to be disruptive. They may troll or insult you, they may spam messages to you in a channel or pm's, and sometimes they may try to flood a channel that you're in. Luckily, IRC comes with a tool to rescue you from these situations by actually preventing that user's text from appearing on your screen. This can be achieved by using the ignore command. If people are flooding channels with useless text or they are otherwise harassing you, the wisest response is to ignore them. Ignore can be set to a nickname or by specifying a user@host format. You can also use wildcards.
/IGNORE [nickname] or [user@host] Ignore all contact from the specified people. So, for example, let's say user 'troll' is trying to start an argument in a channel and there's no OP around to handle him, you would simply:
/IGNORE troll
You should then get a message saying:
*** Added troll to Ignore list
/IGNORE
and you should see a message saying something to the effect of:
*** Ignore is ON *** Ignoring: *.*@*.comcast.net *!*ap@159.88.10.72 *!*troll@*.comptel.com troll
Finally, if you'd like to remove someone from your ignore list so you can see their text again just type:
/IGNORE troll
and you should get a message saying:
*** Removed troll from Ignore list
If your client does not have the /ignore function, there is a server side option available to you. It's /silence or /quote silence and is used in the same manner as ignore, the only difference is that you will need to reset the silenced users every time you connect to the server.