These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Moral Event Horizon: Jane appears to have crossed this with her attempted murder and systematic abuse of Blanche, and her killing of Elvira. The twist ending reveals all this to be a subversion.
Reality Subtext: Davis and Crawford had been rivals since the '30s and utterly despised each other in real life; in his Great Movies essay on the film, Roger Ebert speculated that "it's possible that each agreed to do the picture only because she was jealous of the other's starring role."
Unfortunate Implications: When an aged Carol Kane appears on the DVD's documentary on the film "Bette and Joan: Blind Ambition", she looks and sounds eerily like Baby Jane, right down to the brassy whine.
Values Dissonance: When Edwin's mother is telling him about the night Jane supposedly tried to kill Blanche, she describes the worst part - read: worse than trying to murder her own sister - as being found in a hotel room with a man she didn't know.
Woobie: Jane. Poor, poor Jane. Wracked by guilt over something she never did.
Jane as a child qualifies too. It's strongly implied that their father pushed her into show business and allowed her to become the arrogant brat she was. He never disciplined her and made Blanche think she was The Unfavourite.
Blanche, over the course of the movie, culminating in her supposed death at the end.