You can always explain in a few words why, even without stating your actual underlying reasons. The clerk doesn't need all the details. This person clearly struggled more than he had to if he would have just provided a reason the clerk could understand. I bet his lack of social skills and perceived "stubbornness" were a much higher contribution factor to the clerk being puzzled and may be even thinking he was being stupid.
Are you really that smart if it takes 10 minutes to justify buying the computer with the smallest box?