A tip for anyone who hasn’t tried this yet: run irssi in screen, and connect to #dragonflybsd on EFNet. You can then resume your screen session at any time after disconnecting and see the backlog, catch people addressing you directly, etc.
Before anyone says it: yes, I know, tmux works too.
Other way is using IRC bouncer such as ZNC or psyBNC.
Or use daemonized emacs session with ERC ;)