childhood friendship- thicker than blood but not tuna fish

I had to laugh tonight as I was tucking smart son into bed. We were talking about his day and he announced he had not sat with his dearest friend, B at lunch, in fact he refused to sit at the same table with him even. What could be the cause of such a fissure in a hard and fast kindergarten friendship founded on a love of legos at center time and the playing of superheros on the playground? He said he just couldn't sit by him or even at the same table... because he brought a tuna fish sandwhich for lunch! My ever tolerant smart son told me he just can't handle the smell. He admitted that whenever his friend B brings a tuna fish sandwich, he always sits at another table. Evidently this has been going on for sometime and B has been lobbying his mother to stop making him tuna fish sandwiches (so he will not be abadoned and ostracized by friend smart son- the fair weather not-if-you-bring-a-tuna sandwich friend) but to no avail. I tried to explian to smart son that B's mother should hardly be expected to change their diet and their lunch making routine to cater to his olfactory whims. I guess we need a lesson in tolerance.