How do you get extremally fat?

Answer 1

There is only one way to increase your weight (assuming you do not have a medical condition related to your metabolism). You need to eat or consume more calories than you burn off. The higher the ratio of calories consumed to calories burned off, the faster you will gain weight.

So to get extremely fat you need to minimize your efforts to burn off calories (i.e. stop exercising and laze around) and you need to increase your calorie intake. Eats gobs and gobs of high calorie foods for a long period of time.