Stump the Christian?

[Esquilax]

Can a theory be disproven?

How about a Law?

Both can, though you're barking up the wrong tree because it's actually easier to disprove a law than it is a theory, owing to the former's nature as a declarative statement of cause and effect. For example, the law of universal gravitation could be disproven by the mere existence of a counter-example to the basic concept of the law, that is that objects of mass attract one another. Conversely, conflicting or unexpected data applied to gravitational theory will most often result in an expansion of the scope of said theory, or an alteration to its general principles. This has already happened numerous times, such as the introduction of general relativity. Scientific theories are far sturdier than laws.

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How would science test, measure and verify the immaterial?

If God is pure spirit, how would science know anything about him purely on the basis of scientific method?

So I point out that you can't just assert something and then demand that we prove you wrong, and your response is to assert the same thing and demand that I prove you wrong?

Edited to add: Incidentally Randy, even if I were to accept your claim outright, that god cannot be tested and is unfalsifiable, the conclusion would not be that therefore there is no need to provide testable, falsifiable evidence for god. It would be that there is no good reason to believe in god. "Evidence is not possible," is not the same as "no evidence is needed." You are describing a failure state, not a special category where success is assumed.