I didn't even realize Beth was supposed to be a psycho until this last episode.
Ya, they foreshadowed that she was an awful person, but they didn't exactly telegraph that she was straight up psychotic.
Hints at Beth's true nature just off the top of my head:
- She was cold, borderline cruel to Jerry in the first season.
Her response to Jerry asking if she loved her was really something.
- Jerry's perception of her and her perception of Jerry was really twisted. Also, her ideal Jerry's perception of herself was as this godlike figure which speaks to an egomania on her part.
- There's just a lot of instances of her ego hurting her family in various ways, and then taking zero responsibility.
But this just suggested she inherited her father's narcissism, not that she is this child sociopath. The only thing that may point to that is how quickly she chose Summer over Morty. She just had like, zero hesitation. For most mothers that would be a painful choice, but she just picked Summer right away and didn't give a shit how Morty would feel.
Also, the line that goes "Am I evil?" "No you're smart" was terrible. I hate that crap and it makes Rick look really stupid
Honestly, my enjoyment of the episode is 100% based on how sincerely they wanted us to take Rick there. There's 2 ways to look at that scene:
1) Rick's a shitty dad who's trying to intellectualize his shittiness and then spread his awful cynism to his daughter and basically tore her away from her family.
2) Rick is a jerk, but he knows what's what. He gave his daughter the greatest gift of all, and his being smart and cool and stuff is totally a positive thing that so much of the audience is meant to relate to and stuff.
There aren't enough face palms in the world to cover my feelings if #2 is what the writers wanted us to take from that scene.