You know you're a knitter when:
You spend an hour explaining the "special" decrease you used along the armhole of a sweater that made it nice and neat to a friend who doesn't knit. (You know they're your true friend when - they let you go on about it and pretend interested.)
Your lifelong dream is to be worthy of the title "Domiknitrix".
You have little "knitting stations" set up all over the house. There's the basket with a WIP in the living room. The yarn and needles in the night stand drawer. The knitting pattern book in the bathroom.
You have enough yarn in your stash to open your own LYS and yet you insist you need more yarn to, uh...finish a project. Yeah, that's the ticket.
You see every single object as something that could be cloaked in a sweater or scarf. (I've actually been cooking and been tempted to knit a cook book slip cover.)