What's the difference between insulin intolerance and insulin resistance?

No difference: Insulin resistance (intolerance) means your tissues do not respond to Insulin very easily and it takes larger amounts of Insulin to overcome this affect and control blood sugar. Doctors talk about glucose intolerance which is related to Insulin resistance and Insulin sensitivity which is opposite of resistance.

One is real: Insulin resistance is where your body does not respond appropriately to the usual amount of insulin, generally in fat cells or muscle, but can occur anywhere. Most common cause is obesity and increasing age, plus infection, steroids, etc can make it worse acutely. Insulin intolerance is not a medical term. It seems to have been used occ by some lay groups, although nonsensibily.