tsundere 

1: being on the surface sharp and sarcastic (tsuntsun) but underneath lovestruck and fawning (deredere); characteristic of a gap between acted out actions and feelings in mind;
2: normally being sharp but at some prompt suddenly becoming lovestruck; hot-cold personality type

そうやって俺のことを気にしつつ、しかし素直になりきれない、そのツンデレtsundereさが今若い男の間で大ブーム！

tsundere by grenciae December 22, 2008

Tsundere 

Japanese slang for one who is not nice and gets pissed off easily on the outside, but deep in the inside, is nice, caring, and gentle at all costs to the main character. It is usually used in anime/manga. The tsundere character usually shows his/her tsundere-ness in the later episodes/volumes/chapters.

Kagami Hirragi from the anime/manga Lucky Star is a great example of tsundere.

Tsundere by MisaTange July 8, 2009

Tsundere 

Tsundere describes someone who isn't very nice, but overtime changes to be nicer.

Or it could describe someone who deeply loves someone but tries to hide it from everyone.

Or it could mean some sadist bitch who beats the absolute shit out of the one she loves.

Boring as all hell main character: You're cute.

Tsun-chan: B-b-baaaaaka!

Boring as all hell main character's stupid pervy friend: What a tsundere.

Tsundere by Everythingphobic everythingist December 27, 2016

Tsundere 

Tsundere is a Japanese term for a character development process that describes a person who is initially cold (and sometimes even hostile) before gradually showing a warmer, friendlier side over time. The word is derived from the terms tsun tsun, meaning to turn away in disgust, and dere dere meaning to become 'lovey dovey'.

IT'S NOT LIKE I LIKE YOU OKAY! -Tsundere

Tsundere by Monika :3 June 11, 2018

Tsundere 

A cute ass boy or girl who doesn’t know how to express their feelings to you so they are mean instead

Girl: hey wanna walk to school together?
Tsundere: uh... sure.. but it’s not like I like you or anything! ..... dummy!

Tsundere by Greatlord Cthulhu November 28, 2020

tsundere 

When a person acts cold towards another before gradually warming up to that person or person who acts cruel to the ones they love also called a lovehate relationship

I think your bully is a tsundere, I mean he totally has a crush on you.

tsundere by otakulove February 21, 2011

Tsundere 

A person usually a girl that gets blushed over little things said by her/his crush and talk non-sense because her/his heart is skipping light speed. Tsunderes change emotions very quickly, I could call them little scary but also cute.

Example:

George: Hey Alice, I liked your performations today in the gym class!

Tsundere Alice: Uhmm.. I mean I.. I THANK you! You.. you weren't baddd EITHER! (Blushed

Tsundere by Writer of Urban Dictionary March 24, 2019