Basic Trope: A (usually) female character who conceals a sweet side with a cranky exterior, or conceals a cranky side with a sweet exterior. Most often occurs in UST situations.
Straight: Summer loves Danny, the school's resident daredevil. Unfortunately, his antics frequently get on her nerves, and she lets him know it. "Danny, you jerk!" Summer also probably denies any romantic feelings for Danny. "How could I like that idiot?"
Downplayed: Summer gets annoyed with Danny a little faster than she does with other people. You have to watch closely to notice it, though. When asked if she has feelings for him, she laughs and denies it.
Summer's best friend, Shrinking Violet Alice, also really likes Danny, so Summer feels she can't act on her love for him. Danny, being clueless, constantly acts in ways that are hurtful to both Summer and Alice, causing Summer to lash out at Danny in frustration.
Summer doesn't want to be in love with Danny, be it his appearance, his interests, etc.; but is, and is desperately trying not to be. The stress causes her to insult him.
Summer has been hurt before, and has sworn off romance, but can't help being attracted to Danny. She tries to suppress the feeling by focusing on his negative traits and insulting him.
Summer has a Jerkass Fašade to keep up, and acting rude to Danny is part of it.
Summer is suffering from a Cartwright Curse, and tries to drive Danny away because she doesn't want anything to happen to him.
Summer is bipolar or has a personality disorder (either borderline or dissociative), which explains why she hates and loves Danny at the same time.
Summer and Danny were in a relationship in the past, and it ended badly. Summer is still attracted to Danny, but pulls away whenever it looks like they might be getting too close to each other, since she hasn't forgotten why their previous relationship failed.
Summer is The Mole and knows better than to sleep with the enemy. So she denies any feelings she might have for Danny.
Summer is eight years old and has her first crush, but she still thinks boys are gross.
Summer puts a lot of effort into being nice to Danny, even though the truth is she can't stand him.
Summer does have a crush on Danny, but rather than admit it to him (for whatever reason: past heartbreak, fear of being friendzoned, possibly hiding her true sexuality), she approaches him as a friend and just wants to be his friend. Unfortunately, that doesn't stop Danny's (or even Summer's) friends from calling her out on it, which pisses her off and leads her to go after anyone who mentions it.
Summer seems to like Danny, but it's later revealed that she never did like him.
When Danny reveals his love for her, Summer instantly reveals that the feeling is mutual.
Danny reveals that he has a crush on Summer, Summer feels like crap for yelling at her and his friends, and learns to accept it.
Danny (for whatever reason) makes her feel less broken but every time she gets comfortable fear snaps her into more aggression.
Parodied: Summer bakes a birthday cake for Danny, with strawberries arranged in the shape of a heart. When Danny notices the heart and comments on it, she hastily claims it was a badly misshapen triangle. Later, she admits that it was a heart... then takes it back. Still later, she takes back the taking-back, which leaves Danny hopelessly confused and Summer no closer to expressing her true feelings.
"Maybe he doesn't seem that into you because he thinks you're bipolar? ...Please put the hammer down, I was just joking..."
Invoked: Summer yanks Danny out of the mess he's gotten himself into this time... and verbally berates him before, during, and after. Little does she realize that Danny does this because he thinks Summer is cute when she's angry.
Exploited: Summer works at a Tsundere cafe. * They exist.
Summer's more forthright with her feelings for Danny, rather than showing her cranky side almost all the time.
Danny find out she's being mean to hide her feelings for him and he approaches her and says, "either come forthright with your feelings or leave, please."
Discussed: "You'd better not get on her nerves. Push her buttons and you'll get it".
Conversed: "I wonder when she's gonna stop calling him names and start saying "I love you?"
Summer's Tsundereness is the result of a mental disorder; their relationship is abusive, vile, and unhealthy for the both of them.
After putting up with Summer's crankiness for a while, Danny finally snaps at her, calling her out on her behavior and telling her to leave him alone before storming off. Summer is stunned.
Alternatively: Summer become really unpopular with her peers because of her "mental instabilities".
Danny goes out of his way to avoid Summer, as her constant verbal (and occasionally physical) abuse gives him the impression that she hates him.
Danny is a Hurting Hero. A particularly vicious tsuntsun moment from Summer strikes him in such a way that it reminds him of some painful tragedy in his past, resulting in the last remnants of his "mental armor" shattering. He then breaks down right in front of her.
Danny starts to literally feel terrified of Summer to the point that he won't go out anymore and run away from her in terror the moment she gets angry at him. This makes Summer start to feel immense guilt for being as Tsundere as she is.
Danny has had enough of Summer's behavior and decides to give her a taste of her own medicine. Whenever she comes near him, he treats her with the same bitterness as she treated him.
Danny's willingness to endure Summer's disorder inspires her to take medication in addition to a concentrated effort to reign in her more violent tendencies. She regularly thanks him for his support.
Summer shows up on Danny's doorstep that evening, and apologizes. A lot. Danny forgives her.
Summer decides to go through anger management to improve herself, and in the end goes from a Type A to a Type B.
Danny reminds Summer of her favourite cousin, who was also a daredevil and who died years ago in a motorcycle accident. She'll never admit this out loud, though, and expresses her concern by be(r)ating Danny every time he does something stupid. (Which is often.)