You know you're a writer when:
1. You constantly churn out ideas for some work in progress wherever you are, even if the ideas don't fit.
2. You can't sleep at night because you are thinking about how to write your next work.
3. You find yourself drawing upon the personalities of people around you (even taking notes, which really freaks people out).
4. You write out ideas and passages (even whole chapters) instead of doing the work at hand.
5. You actually take notes on things you read, highlight passages, even put notes in the margins; everything that seems to give you an idea for writing something.
6. You love reading through other people's work and asking questions about their style and insperation.
7. You ask yourself how your character would deal with a situation.
8. You're never quite happy with you're writing, there is always something that could be better or put in a different way.
9. You speak out loud while writing, trying to figure out what sounds good, how a charater would say something or how they would speak.
10. You try to see how events in the real world could be used in your writing (even taking notes while watching the news, which also freaks people out).