How to get no cavities after not brushing at all?

Pray: If you don't brush and floss, you will most likely get cavities. Change your ways and your bad habits and start now. Get your teeth checked and begin a healthier life style and save money over time. Start brushing and flossing and eat healthy avoiding foods and snacks that promote tooth decay and gum disease. Discuss all this with your own dentist.

Genetics : Be one of he very few people who do not have a genetic predisposition for caries.

Exception?: Not quite sure of the question, but i must say that no brushing leads to cavities and can affect your overall systemic health. By allowing the bacterial plaque to remain in your mouth in unchecked numbers you run a very high risk of dental disease as well as systemic disease. Brush/floss/fluoride.