Person A's stance is that disagreements happen. They seem unbothered. Person B frames the disagreement--amplified by the fact that it apparently means so little to Person A--as disrespect and injustice, and that they're probably a sociopath. Letting the disagreement go means accepting and enabling the behavior, and being tolerant of abuse. Person A and those associated with them are now suspect in all past and future situations. New people must be warned. Person B's fire can burn for years, hijacking their personality and becoming their ruling passion, to the exclusion of anything else they might have accomplished or been known...