A very popular anime stereotype, usually, girls are tsunders, although there are some rare instances where otherwise is stated. Tsundere is a word made up from two other words, "Tsun Tsun" and "Dere Dere". Both terms describe acts of a person. "Tsun Tsun" is used for cold or rather blunt behaviour, meanwhile "Dere Dere" is used when a person becomes shy or flustered in front of their lover/crush.
How to know a character is a tsundere:
they will act mean to their crush while blushing or being flustered
pouting/ "hmph!"
usually.. they're short
usually.. a girl
stomping
they're called, "Hiyoko"
Oh my gosh! Osana, you are just SUCH a tsundere. Kyahahaha, it's funny seeing you so mad like this!
The girl equivalent of a frenemy. Except on their friendly side, they have (although a low chance) or eroticism...
bro: nah my digital footprint is def a tsundere
df: HOW COME BAKA!?!? I AM NOT A TSUNDERE!?!?
Islamic Republic of Iran: Ha ha ha... we hath came, for the immigrants shall
df: Sorry.... i am a tsundere.... just spare us please....