I'm sure that those of you reading this, are expecting me to write a list of all the things that shouldn't be written about in fanfic...

I'm not going to make a list. Instead, I'm going to give you some things you should think about BEFORE you write. 

STEREOTYPES: Is what I'm writing creating stereotypes about a certain group of people? Is what I'm writing encouraging people to believe already existing stereotypes?

OBJECTIFICATION: Is what I'm writing objectifying a certain group of people? Is what I'm writing make certain people/characters seem less human?

ROMANTICIZING: Is what I'm writing romanticizing drug use, rape, etc?

RELATIONSHIPS: Is it unclear that the relationship the characters are in are unhealthy, and should be changed? Is what I'm writing encouraging people to stay in unhealthy relationships? 

^^^^^^If any of these fit, do some editing! You don't have to delete your story! 

OVERALL JUST THINK: IS WHAT I'M WRITING OFFENSIVE, HURTFUL, OR MISLEADING?

None of us are perfect. We may write about such things, and not even realize what we're doing... Just learn from it. Admit to yourself that you made a mistake, and try your best not repeat your mistake. 

:)