Well I have an idea of what you want to do, however I doubt your example is what you want to do so let me verify. You will have a swear.txt that lists all the swear words? The reason I ask is (even if isin worked for files) that still wouldn't work:

$1- hey how are you
swear.txt = damn
if ($1- isin swear.txt)
That would mean
if (hey how are you isin damn)
So I assume you meant it the other way around? Check if words in the file are in the user's text?

In which case you'd need to use $read, and check if $1, $2, $N are in swear.txt using a loop:
Code:
var %i = 1
while (%i <= $0) {
   if ($read(swear.txt, ns, $eval($chr(36) $+ %i,2))) {
      ; kick the user
      break
   }
   inc %i
}


Something like that should work, note however I didn't actually test that.