There will probably never come a day when you need to pitch an anime series in one sentence, but alternatively, there might come such a day. You never know when you are going to meet the rare type of fan so busy that they only watch a new series if they can be successfully persuaded by how it is summed up in one sentence.
Kimi ni Todoke
Two dense people fall in love with each other and it takes two seasons for minimal things to happen.
Spice and Wolf
Everything you ever wanted to know about medieval economics.
Ouran High School Host Club
Rich people doing whatever they want while being extraordinarily fabulous.
Neon Genesis Evangelion
Adults put the fate of the world in the hands of teenagers, and does not get the results they expected.
A boy’s right hand is stronger than his left hand, but not for the reasons you think.
Trying to kill your teacher is the only way to turn you into a well-adjusted adult.
Love, Chunibyou, and Other Delusions
Endlessly facepalming when the poor decisions from his youth are personified as a cute girl that is obsessed with his past self.
From the New World
A group of kids discover evolution.
Akame Ga Kill
I hope you weren’t attached to any of these characters.
Incredible power, but it will cost you an arm and a leg.
A couple yelling each other’s names until the enemy gets so sick of it they die in one strike out of pure spite.
The personification of the meme: motherfuckers beating people with other motherfuckers.
Kodomo no Jikan
Thinly-veiled lolicon hentai that had more seasons than most of your favorite anime series.
Classmates fail to share critical information and pay dearly for it.
A cowardly boy and his yandere stalker play Hunger Games.
Alcohol leads to epiphanies and definitely not more problems.
Misfits become pirates to hunt for treasure then get sidetracked for about 700 episodes.
There is no problem you can’t eat your way out of.
One Punch Man
Completely owns the shounen trope that most fights are wrapped up in one decisive punch anyway.
A child’s card game gets deadly serious.
Puberty-riddled teen tries to get his leg over AND not die in his survival game.
A happy show about magical girls right up until it isn’t.
Attack on Titan
Proof that a large cast is just an excuse to kill more people in fun ways.
A city kid who realizes that cute animals need to die in order to make delicious food.
Kill la Kill
The slow realization that nudity is the path to ultimate power.
Sword Art Online
A solo MMO player that somehow doesn’t die and gets all the chicks.
A smart MMO player that DOESN’T run off on his own and instead forms a party to not die.
A guy gets sick of his pseudo-sexual relationship with his boss, leaves, and causes the world to end.
It is all fun and games until someone loses a head.
There is no heaven or hell, only high school.
High School of the Dead
Chances are good you will survive the zombie apocalypse if you are a girl, have a large bust, and no qualms about showing a lot of skin.
High School DxD
Who needs plot when you have cleavage?
My Hero Academia
A normal kid sucks until he inherits a superhero power, and then…Still continues to suck for a long while.
If you pick up babies that pop out of old people, you are responsible for them.
Everyone in town has a really weird story.
A boy fights his feelings for his sister then pursues her young friends.
The Ambition of Oda Nobuna
Girls, girls rule the world.
Boys won’t like you if you are taller than them until they decide they do.
Everyone switches bodies and then can no longer harbor secrets once they have seen each other’s genitals, probably.
B Gata H Kei
What happens when a girl is thirsty, but doesn’t know how to initiate.
A bunch of kids hang out at an older man’s house and everyone is okay with it.
Only one person can solve this mystery and everyone else is stupid.
Not everyone can be the hero of their own story.
Engaged to the Unknown
A love story that is barely about the main couple at all.
It is true that you can beat-beat-beat your problems away.
My Love Story
A boy that got hit with every branch of the ugly tree in his face finds love because he has a good heart.
A boy realizes that pretty girls will only like him after they are dead.
Yuna Yuki is a Hero
Creators trying to see how close to Madoka Magica they could get before they get in trouble.
Fist of the North Star
People get touched in bad spots and die.
Samurai are as awesome as Japanophiles think they are.
Higurashi: When They Cry
Girls are more murderous than they look.
The Melancholy of Haruhi Suzumiya
God is a selfish teen girl.
Some of these were fragments, and I am sorry for it. I know you have some good ones, post them in the comments section below.