Derp!  I am really weird and funny but write a lot of dark stuff. 
You Know You're a Writer When:
You have the last chapters of a story done before even thinking of the characters names.
You often imagine your books becoming movies.
Spell check is your best friend.

Not being able to write is like not being able to pee to you... you just can't hold it in for so long.
You write so fast, you leave out words in a sentence.
Things that are written badly annoy you and make you want to re-write it better.
You laugh at jokes you wrote yourself.
You can spell words like 'troublesome' but can't spell 'the' half the time.

When you have to write some sort of story in class, you get carried away.
You would rather die than use words like 'good' or 'nice' and etc.
You put off the last chapter of a story simply because you don't want it to end.
If a story, movie, show, etc. finishes without closure, you have a powerful need to write a suitable ending.
You like to fidget, tap, or chew on the tip of something when you are trying to come up with a new sentence, paragraph, chapter, or story.

You dream of new stories.
You often revisit some of your old stories.
Someone can call your name twenty times without you hearing if you're writing.
You would rather write than go out.
Your/you're and their/there/they're are errors that send you into an apoplectic fit.
You get cranky if you don't get to write.
You've heard/seen/thought something, and thought, I need to write that down.
You wake up in the middle of the night and scrabble for a pen and paper you keep next to your bed to write down a scene to make the voices be quiet so you can get some sleep.
Getting the scene finished is more important than coffee, the bathroom, or food.
A blank wall becomes the screen where the scene you're writing takes place right in front of your eyes.

You've apologized out loud to a character after doing something horrible to them.