When it's literally the thing you think about most. :D
When you always go out with a toy sonic screwdriver in case some monsters arrived and you need to save the day... (I'm doing that... only 1 person has noticed that it's from Doctor Who!)
When you got your cousin and best friend to be obsessed with Doctor Who (okay, my cousin only likes it because she thinks the Doctor is cute)
When you had a major argument with your friend because they wouldn't accept the fact that his name isn't Doctor Who, it's the Doctor.
When you get up super early to catch an hour of Doctor Who before school.
This is AMAZING!
You buy life-size cardboard cut-outs of the characters and throw them birthday parties...!
When you think your air-conditioning (momentarily) sounds like the TARDIS materialising... :P
you're watching the Timey-Wimey Special
when you spend every night dreaming of going on adventures with him and your days are spent listening for the tardis vwarp. yeah... then you know your obsessed.
You know when you are obessed to Doctor Who when you want to paint the door to your room like the outside of the police box so your room can be a TARDIS. And the color of your door has to be TARDIS blue.
When you pass a statue and you can't help but to force yourself to not blink in the silent fear that it might be a weeping angel..