I was also going to say food. I get obsessed with the "fancy" coffee drinks from time to time. They are not only bad for ones waistline, but bad for ones pocket book as well.
Also my job. I can't tell you what I do, but let me just say that every day we all go home to our families alive and well and not in a body bag is a good day! I am, to a degree, obsessed with portions of my job. There are tasks I detest, but the main part is something I'm interested in which can lead to marital discord as it leads me to go to work at night sometimes for hours. I went last night (saturday) from 9pm till 2 am. It's so nice to be able to go and do the parts I like (don't worry not doing anything hazardous at 1am, not allowed to do that stuff with anything less than 12 people and a medical staff) with no one else around to bother me, no distractions, and no noise. Manager loves it, husband hates it. So I guess this might be unhealthy in terms of the marriage and the lack of sleep (I'm on my 3rd cup of coffee). And during the day the fact that the job is kind of dangerous.