First of all you can consider me momentarily deranged:

WHY in every single fic where Ranma's girl side becomes a person that when
the female half stands around the male half assumes they are boy&girl friend
or that they are engaged.  

Let's look at the thought process:

They act the same
Share the same facial features
Share the same hairstyle
both share the same sport/occupation
etc. etc.

Wow, they must be romantically involved.

Wrong.   Wouldn't a normal person assume that THEY ARE RELATED maybe even
TWINS?   

Well thanks for listening to my ranting

Deunan