With the understanding that donuts are bad in general, eight donuts in one sitting is much worst than eight donuts throughout the week. This is because in one sitting, it would raise your blood glucose (sugar) level extremely high and dangerous levels. Spreading the bad carbs (which donuts are) over a long time span would still raise your blood sugar after eating it, but the level will not be so high that your body cannot manage it (assuming that you are not insulin resistant or have metabolic syndrome).
The reason why donuts spike (raises) your blood sugar is because it is refined carbohydrate. All carbohydrate raises blood sugar. High-glycemic carbs (such as refined carbohydrates such as donuts) raise it even more.
A rise in blood sugar causes the body to pump out insulin in an attempt to shuttle the glucose into the cells for energy. If one is insulin resistant, or eat a high glycemic meal (like 8 donuts), the insulin is not able to move the sugar into the cells fast enough. The glucose remains in the blood stream and spread to all parts of the body. High glucose levels is damaging to all organs of the body. Furthermore, the body then converts these extra sugar in the bloodstream into fat.
If you constantly eat like 8 donuts, the body will become "insulin resistant" which is a characteristic of "metabolic syndrome". This eventually leads to diabetes and is one of the causes of the obesity epidemic. Diabetes, by definition is "high blood sugar". Glucose is just another name for sugar.