I know that hydrogenated oils and caffeine lower insulin sensitivity. Saturated fats? Ephedrine? What else???
Eating lots of refined high glycemic or high insulin index carbs will decrease your insulin sensitivity. But nothing will decrease your insulin sensitivity like gaining some extra body fat.
You’re heading in the right track; suffice it to say that any stimulant will decrease insulin sensitivity. Obesity will decrease it as well, as the more fat cells a person has, the less sensitive to insulin they become (the premise behind the diabetic cycle).