From Compsci.ca Wiki
The rules are simple. Find someone who is regularly in the channel (but isn't at the moment) and take their name. Bonus points if nobody notices right away.
Try taking somebody's name when:
- You want to talk to them but they aren't responding to nick-notifies. (Add numbers for IRC to allow it: eg, "Hikaru79 -> Hikaru80")
- Somebody gets kicked out of the channel as a joke
- net splits
- Somebody has to reboot and says "brb"
- Somebody left their own name to take somebody elses' momentarily (This one is CRUCIAL, and works well recursively: ie, you person B takes person A's name, person C takes person B's name, ...)