you can use IRC through CGI irc (google it) if you have a host with CGI support. This will allow you to chat on IRC from anywhere as long as you have internet access. No need for java, proxies, anything; just web access. It cannot be blocked unless they block the entire http protocol.
but just keep in mind that any activity you do on someone else?s computer can be monitored, and all they have to do is check your browser history to see that you have been chating on IRC. depending on your TOS it might not be that big of deal, the main reason IRC is prohibited is probably not to stop you from wasting time and saying "lol" a lot, but because going on IRC opens up your network for attacks. If you piss someone off they have your IP and can and will retaliate. Just look at the myg0t attacks on our server. CGI irc uses your webhost's address so your network is never actually exposed to the IRC protocol and you are not susceptible to any attacks (but your webhost running CGI irc is). It?s not really anything to worry about though on ;0 when your biggest threat is Duo speaking nonsense that both intrigues and confuses.
at any rate if u want to know more about CGI irc PM me or something, but system admins aren't as stupid as you think and it's probably not worth losing your job over bypassing the system to do something as silly as chat.