Depends on the IRC server. Freenode's old IRC daemon was very liberal about the IRC protocol. If you "accidentally" included "POST /whatever HTTP/1.1" before the IRC commands, the server would be just fine with that. You could also send commands without acknowledging responses. This meant that an arbitrary HTTP request could create an IRC connection and send stuff to channels!

The result was a web page that merely visiting would spam people on the IRC network with hate messages from your IP. It was amusing.