$iif is mostly used for minor variances in a string, and not the best choice for your situation.

on @15:text:!* :#: {
  if ($1 == !die) part $chan
  elseif ($1 == !fart) describe $chan lets one rip $iif($2 ison $chan,at $2) $+ .
  else notice $nick Nope, Access Denied.
}

You can see where I used $iif to add "at somenick" if the user typed !fart somenick.
If they don't specify a nick, then nothing else is added. (no false condition is required)

- Raccoon


Well. At least I won lunch.
Good philosophy, see good in bad, I like!