Yandere/Playing With

Basic Trope: The Cutie falls madly in love and goes to insane lengths to keep their Love Interest.
 * Straight: 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.
 * Exaggerated: Bob says "Hi" to Alice. Sweet little Sally flips out and tries to choke her with her hair ribbons.
 * Sally notices some shipping of Bob and Alice, even though they've never really met. Sweet little Sally flips to  aggressive mode and overdoses Alice's sleeping pills in her sleep.
 * Downplayed: Sally repeatedly tries to drive wedges between Alice and Bob, but it never escalates into violence.
 * Justified: 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 has Borderline Personality Disorder.
 * Inverted: Sally has obvious problems, but her immense love for Bob gives her some much-needed stability.
 * Sally, normally sane and nonviolent, lashes out at Bob after he fails to understand the word "no".
 * 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.
 * Sally acts like an insane person towards Bob because she really likes him on the inside.
 * Subverted: When Bob chooses Alice, it looks like Sally might crack, but she happily declares I Want My Beloved to Be Happy.
 * Bob is constantly bothered by crazy women, so he happily puts up with Sally because she keeps other potential admirers away.
 * The only reason Sally is targeting Bob is because it's Alice she's after, and she wants Bob out of the way.
 * Double Subverted: ...But then she secretly poisons Alice's drink.
 * ...which hardly solves the problem, since Sally herself is crazy enough for ten women, but Bob doesn't want to risk his life by upsetting her.
 * But it turns out that Alice is just crazy about Bob, and she sees Sally as a threat to their relationship, and decides to take care of her.
 * Parodied: Sally is a Grotesque Cute Devil in Plain Sight, but nobody notices.
 * Deconstructed: 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 abandonnement, 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.
 * Reconstructed: 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.
 * 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...
 * Averted: Though jealous, Sally does not consider genuinely insane solutions to getting between Alice and Bob.
 * Or maybe she just wants them dead for the hell of it.
 * 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?"
 * Lampshaded: "Oh, sure, Sally seems sweet enough. But I dunno, she seems kind of... off..."
 * Sally: "I'll do anything for our love, Bob. Anything..."
 * 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.
 * Exploited: 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. He has a thing for yanderes, knows that Sally is one and starts dating with her to keep other girls away from him.
 * Defied: 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.
 * 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."
 * 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.

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~