The unforgivable political sin is vanity; the killer diet is sour grapes.

Neil Kinnock’s quote, "The unforgivable political sin is vanity; the killer diet is sour grapes," uses metaphor and humor to make a point about politics and personal behavior. Kinnock suggests that in the realm of politics, being driven by vanity—or self-absorption—is a critical flaw that undermines a leader's integrity and effectiveness. The reference to sour grapes speaks to the idea that when people can't achieve what they want, they often turn to resentment or bitterness, symbolized by the metaphor of rejecting something simply because it's unattainable, much like the story of Aesop’s fable of the fox and the sour grapes.

The meaning behind the quote is that vanity, especially in politics, leads to actions and decisions based on personal ego rather than the public good. Kinnock is emphasizing that those who are more concerned with their image or self-interest are less likely to make fair or meaningful political decisions. The second part of the quote, the "killer diet," suggests that the bitterness or rejection of something because it’s not achievable, like sour grapes, is a self-destructive approach to handling personal or professional disappointment.

Originating from Neil Kinnock, a British politician, the quote reflects his experience and observations in the political arena. As a prominent figure in the Labour Party, Kinnock was often involved in debates about leadership, responsibility, and the importance of integrity in politics. His use of vanity and sour grapes captures his critical stance on political figures who focus more on their image or personal gain than on genuine service to the public.

Ultimately, Kinnock’s message critiques those in politics who are driven by self-interest and vanity, warning that such behavior can be detrimental not only to their political careers but also to the broader political system. His mention of sour grapes adds a layer of caution about letting personal bitterness cloud one’s judgment, encouraging a more self-aware and balanced approach to leadership and decision-making.