On Mon, 20 Apr 1998, Dave Eddy wrote:

     Akane just shook her head and shrugged, but she relaxed a
little.  Ranko tilted her head as a thought occurred to her,
ignoring Akane's slightly awkward expression.  "Say, that reminds
me.  Tell me about Ranma-oniichan.  Why do you call him a
pervert?  Does he go around sniffing used underwear or
something?"

Umm, Akane calls Ranma a pervert because that's a Japanese pun, since "hentai"
can mean "transform".  All characters who know of the curse would be instantly
aware of this.