I guess I would have to say that my worst dieting experience was the time I went to a diet doctor (a la Dr. Bernstein). He put me on a low carb diet that was also very low calorie.. about 750 a day and a big handful of vitamins. Little skinny nurses weighed me in twice a week and showed me plastic foods to help me learn portion control. I met with the great doctor once a month and when I stopped being able to stick to his diet after a few weeks, he declared that I had emotional problems and would never successfully lose weight until I dealt with those. Um.. ok.

I too did lots of horrible diets, but that was the most degrading, I think.