Try opening an account with a sufficiently obnoxious name eg. KidBeater@yahoo.com. I'm about to give it a go and see if that works..... yeah, it does.
The next thing to do is start up some kind of rapport with your audience ie naive americans. Prove that the divide between Anglo-American humour is as huge as it always has been by offending them in as sick a way as possible. Part One is your screename which is why this is so important.
As Adolf Hitler always said, Repetition puts the point across. So say hi by flooding the screen for a while. There is a nack to this without getting chucked off but it doesn't take too long to master. Of course, there is a danger in that a fair number of the room will now ignore you, which means they will not see your future messages anymore. Those with thicker skins will stay on and, hopefully, fight back with great wit. That's the idea anyway.
Sometimes a bizarre phenomenon occurs in a chat room where no matter how disgusting you are, someone still really wants to chat to you. These people should not be ignored - these people are sensible and will quite often be on your side - value them. They are also usually the source of a worthwhile and, uncommonly, interesting chat.
That's the basics. Since Geocities merged, there are now thousands of chat rooms which is rather unfortunate. This means that most of them are pretty empty or full of people talking privately amongst themselves - not good. Have patience and you may strike gold. It's been a while though.
To conclude, my number one tip is DO NOT TAKE CHATROOMS SERIOUSLY, that will be your downfall.