Basic Trope: A seemingly harmless character falls madly in love and goes to insane lengths to keep their Love Interest.
- Sweet little Sally loves Bob... so when he picks Alice instead, she tries to get rid of her.
- Sally attempts to kill anyone shows any interest or could possibly harm Bob.
- Clingy Jealous Girl/Crazy Jealous Guy
- Sally is shown to be mentally unstable, but she's relatively benign. At best, she's given a would-be hypotenuse a few ineffectual death threats, but she's never actually carried it out. At least that we know of.
- Sally is a Dogged Nice Girl and Stalker With a Crush to Bob and viciously assaults anyone who harms him. However, she's willing to be in a purely platonic relationship with Bob if that's what will make him happy.
- Sally has been abandoned and alone all her life, and Bob was the only one who made her feel loved and special.
- Bob is a Manipulative Bastard who passes himself off as a nice guy, and maybe even honestly believes he is one. Over the course of his relationship with Sally, he's gotten her to center her entire life around him, which has in turn caused her to become a Clingy Jealous Girl. Then Bob—possibly oblivious to the fact that he ought to have expected this outcome—dumps her for Alice because Sally's become a Clingy Jealous Girl.
- Sally is a psychopath and a narcissist. As result, she needs to feel loved to maintain her high self-esteem. Bob is the only person who loves her as much as he did and because of this, she is willing to go to insane lengths to keep him all to herself.
- Sally has always been Ax-Crazy, even before she met Bob.
- Sally thinks that killing people who get in the way of your love is what you're supposed to do.
- Sally is normally nonviolent and sane, except around Bob, who seems to be a walking trigger for her.
- Sally is normally sane, but acts insane, as she wishes to be hated by Bob. One day, Bob says he doesn't hate her, at which point Sally does anything to get Bob to hate her.
- I Want My Beloved to Be Happy. If Bob's truly happy with Alice, who is Sally to rip them apart because of her own desires?
- Sally is normally Ax-Crazy until she meets Bob, who is an emotional anchor in her life.
- Subverted: When Bob chooses Alice, it looks like Sally might crack, but she happily declares I Want My Beloved to Be Happy.
- Double Subverted: ...But then she secretly poisons Alice's drink.
Bob: Hey? What happened?
- Sally is standing over Alice's dead body, when Bob walks into the room...
Sally: It was only to protect you, sweetie.
Bob: What the hell are you doing with that dead body?! I. THOUGHT. YOU. LOVED. ME!
Sally: I DO LOVE YOU! Why else would I bake your dog into my lovely pie?
Bob: That dog doesn't love you!
- Sally kills a dog because it was trying to hump Bob's leg.
- Sally, a butcher's apprentice, is rejected by Bob but takes it rather well. But whenever Bob sees her after rejecting her, it's always with a bloody axe and a grin from the meats she's cutting up - and he panics for the imagery in his own mind.
- Zig Zagged: Sally's views on what Bob can or can't do seem to depend greatly on how she's feeling at the moment; she may declare that she wants her beloved to be happy in one episode, only to crack with the pressure the next episode and almost kill Alice before realizing what a terrible thing she was about to do to Bob's happiness; in the next episode, she witnesses a fight between Bob and Alice and decides that he'd be better off without her...
- Enforced: "How are we going to make Alice and Bob the Official Couple when we don't have someone to pair Sally off with? We can't just kill her off..." "Have her go nuts?"
Sally: "I'll do anything for our love, Bob. Anything..."
- "Oh, sure, Sally seems sweet enough. But I dunno, she seems kind of... off..."
Bob: "...You mean that 'love you to death' thing literally, don't you?"
- Invoked: Bob is a psychopathic narcissist who deliberately manipulates Sally's fragile psyche and love for him to achieve the extreme ego boost of having someone as sweet as her snap out of sheer need for him and do horrifying acts she would never consider in a rational state of mind.
- Alice, a Bitch in Sheep's Clothing herself, sets Sally up to look unstable and deliberately sets off her Clingy Jealous Girl instincts in order to drive a wedge between her and Bob.
- Alternatively, Bob has a lot of girls chasing him and is getting fed up with the overwhelming attention. He has a thing for yanderes, knows that Sally is one and starts dating her to keep other girls away from him.
- Or, Bob is in a situation where everyone is trying to kill him, and with Sally as handy with an axe as she is, he'll take whatever help he can get.
- Sally and Bob have a long talk about their feelings, then Sally decides I Want My Beloved to Be Happy.
- Sally knows she has a metaphorical screw loose and issues when it comes to romance, so she starts seeing a therapist when she meets Bob.
- Sally, knowing how clingy she gets, decides that she and Bob are Better as Friends.
- Bob is aware of what Sally is, so dates her to get her to see a therapist and stop her doing more drastic options.
- Discussed: "Have you ever noticed the way Sally's eye starts twitching when Bob talks to Alice? It's really creepy."
- Conversed: "Oh great, this show has a love triangle. These things almost always end with the odd one out either gracefully giving up or boiling a rabbit. And just giving up doesn't exactly make for drama, so we might as well say goodbye to Flopsy right now."
- Sally is in love with Bob. One day Alice threatens Bob, and Sally discovers this. Alice is never heard from again.
- It's implied that Sally has a crush on Bob.
- Sally's instability is due to Bob keeping a Betty and Veronica situation going on for too long without considering either girl's feelings beyond "Awesome, two chicks dig me!".
- The only thing that renders Sally insane is her fear of abandonment, and even otherwise, Danny insists she should be treated with compassion. He comforts her, and she succeeds in her attempts to overcome her abandonnement issues, avoiding to have been slowly driven completely mad. She drops all violent behaviour, realizes that Alice is the best for Bob, still wants her beloved to be happy, and retreats. Even Danny and her might get their happy ending... together.
- Bob dumps Sally after he finds out about what she did to Alice.
- And when Bob finally gets around to picking Alice, Sally's unrequited feelings cause her to Murder the Hypotenuse.
- Except Danny is now jealous and can't bear that she has become geniuely Just Friends with Bob. She can't bear that he did the same with Alice. One of them ends up cooling down. The other creates unsettling fantasies to entertain oneself. What if a minor accident...
- Bob is also a Yandere. He and Sally get Danny and Alice to kill each other so Bob and Sally can be together.
- Played For Laughs: Bob has no clue that Sally loves him; she makes several cartoonish attempts to break them apart, only to push the pair closer together.
- Played For Drama:
- Only the audience is aware of Sally's instability, and watch it develop and worsen as Bob and Alice grow closer, unaware that every sweet moment they share drives Sally closer to the edge.
- Alice is Sally's best friend. Sally feels ashamed and guilty for wanting to harm her best friend and her love interest, but with each nice thing Bob does for Alice she finds it increasingly difficult to keep such thoughts away.
- Sally and Alice (and possibly Bob) get caught up in a brutal fight since Alice was able to dodge the immediate attack from Sally. However, through Sally's screams Alice (and/or Bob) realizes why Sally's attacking her, and they are conflicted about how to respond amidst the carnage because even though if Sally were to die it'd be justifiable self-defense, Alice (and/or Bob) may not want her death on their conscience - they may even be desperate to try to find a way to calm Sally down enough so that she can get proper therapy rather than just kill her.
Oh, are you finished playing with this trope already~? That's fine, as long as you go back to Yandere, my love. And don't you dare go to Tsundere or I'll slit your fucking throat~