If you go to a social event and all you can think about is getting home so you can knit (me, tonight).
If you take your Patternworks catalog to bed with you every night and fall asleep dreaming of yarn.
If you have a million other things to do but just keep telling yourself "Just one more row...."
If your children's new favorite game is "how to get all tangled up in mommy's new yarn."
If you get upset when your cat drags a new ball of yarn out of your knitting bag and drops it in the living room. Not because she messed up your yarn (she didn't) but because you didn't want your dh to know you'd bought more yarn.
If all your internet bookmarks are for knitting sites or free patterns.
If you can't think of anything new to talk about with people b/c all you do and all your think about is knitting.