[<channel>] <nick|hostmask> [<expires>]
If you have the #channel,op capability, this will effect a
persistent ban from interacting with the bot on the given
<hostmask> (or the current hostmask associated with <nick>). Other
plugins may enforce this ban by actually banning users with
matching hostmasks when they join. <expires> is an optional
argument specifying when (in "seconds from now") the ban should
expire; if none is given, the ban will never automatically expire.
<channel> is only necessary if the message isn't sent in the
channel itself.