You can use $regsubex to do the same thing efficiently:

vowels {
  var %vowels = $regsubex($1-,/[aeiou]/gS,)
  me takes all of the vowel letters out of $$1-'s nick! Without the vowel letters, $1-'s nick looks like %vowels 
}

Although I think it's better to make it open to all sentences, not just the nick:

vowels {
  var %vowels = $regsubex($1-,/[aeiou]/gS,)
  me takes all of the vowel letters out of the sentence $+(",$$1-,") $&
    Without the vowel letters, it looks like: %vowels 
}