It's a nickname for a special Girl.
the most awesome person ever. shes so much fun to hangout with and i love her<3. shes like one of the prettiest people i know even though she wont admit it. we can crack up at the stupidest things for like an hour. she is really easy to talk to but she has a loud mouth

An exclamation made when your friends or family are teasing you to a point where you can't handle it anymore and a hissy fit is in order.

Derived from a YouTube user's famed outburst following Britney's lackluster performance at the 2007 VMA's.

MAL, an abbreviation for the site:
myanimelist.net
A site with synopsis of anime and manga and where many otakus discuss anime.

Mal Is a name for a beautiful person, personality and body-wise. A Mal is the type of girl with an amazing sense of humor, and she loves meeting new people. If you ever get to know a Mal, respect and cherish them. They're quick to make decisions and will not hesitate to leave you if she needs to. A Mal can come off as rude, but really they're a wonderful and charming person. They flirt with everyone, so don't be upset if she flirts with someone other than you. Mal's are extremely attractive and great conversationalists. They always try to pick up their friends' hobbies, and conquer their fears with ease. If they get a bit mad at you, just give them time to cool off. They're pretty stubborn but also pretty adorable.

to be mean or {evil}

(noun) Short for Mallory.
Australian adolescent female, also known as 'a funny fucking legend/champion'.

Mal:
(1) A man whore
(2) Someone who plays with women