paste all this into aliases in tools>scripts editor
-----------------

/afk {
  if (!$1) {
    set %away.reason $null
    set %away.afktime $ctime
    ame is now AFK. Reason: %away.reason
    set %orgnick $me
    nick $me $+ |AFK
  }
  else {
    set %away.afktime $ctime
    set %away.reason $1-
    ame is now AFK. Reason: %away.reason
    set %orgnick $me
    nick $me $+ |AFK
  }
}
/BRB {
  if (!$1) {
    set %away.reason $null
    set %away.afktime $ctime
    ame will be right back. Reason: %away.reason
    set %orgnick $me
    nick $me $+ |BRB
  }
  else {
    set %away.afktime $ctime
    set %away.reason $1-
    ame will be right back. Reason: %away.reason
    set %orgnick $me
    nick $me $+ |BRB
  }
}
/back {
  ame is back from %away.reason $+ . Gone for $duration($calc($ctime - %away.afktime )) $+ .
  nick %orgnick
  unset %away.*
}


Usage:
/afk reason
/brb reason

/back