When you freak out becasue you found a store in your area called The Eleventh Hour while you were listening to the Doctor Who soundtrack on your iPod.
That's not obsession, that's just awesome!
When you make snow daleks instead of snow men. :)
You are obsessed with Doctor Who when:
1) You are scared of plastic
2) You stare at the sun and think about when it will explode
3) You start seeing the TARDIS on the corner of your street
4) You hate all big, green things
5) You are scared of dirt
6) You devise schemes to trap the Doctor so you can talk to him
7) You try to make a sonic item
8) You hate all volcanoes
9) You avoid all statues
10) You start talking about him to random people on the street
When you find a reference in what people say every 5 sentences even when they don't watch Doctor Who.
When you have two shadows and pray to god that the Vashta Nerada won't eat you now.
That happened to me last night.
I've got a "Trust me, I'm The Doctor" t-shirt to wear on my doctoral thesis defense...
YOU are a hero.
when you find a way to weasel a quote or fact into any assignment
When you smash your insanely creepy angel statues that you've had for years the second after seeing blink.