rc stands for 'run commands.' this has the phrase 'man' in it and is therefore unsuitable for feminize(1). use sed instead.

rc/bin/feminize

@@ -1,3 +1,5 @@
-#!/bin/rc
+#!/bin/sed -f
 
-exec sed 's/ [aeiou]n([a-z][a-z][a-z])/ man\1/; s/ [a-z]em([a-z][a-z][a-z])/ fem\1/; s/ [aeiou]m/ fem/;'
+s/ [aeiou]n([a-z][a-z][a-z])/ man\1/
+s/ [a-z]em([a-z][a-z][a-z])/ fem\1/
+s/ [aeiou]m/ fem/