When every vacation you have planned for the next 12 months involves diving somewhere.
When the arguments you have with your spouse concern diving techniques and buddy behavior.
When you find yourself skipping opportunities to ride (or golf, or whatever your previous passion was) in order to go diving.
When the thing you hate most in the ENTIRE WORLD is being cold, and you voluntary immerse yourself on a regular basis in ice cold water long enough to start shivering.
I'm also guilty of the LDS knowing it's me; scheming to hide purchases of dive equipment from the DH; talking diving until our prior, non-diving friends' eyes glaze over; spending every bit of down time at work perusing scuba-related stuff on the internet -- and what's worse, I didn't do any recreational reading over the summer that wasn't about diving!