maybe something like 'personal antipathy' to emphasise that someone's own feelings may be colouring their objective judgment... it depends exactly how you want to use it.
'Sour grapes' comes from the fable of the fox who tried to reach some grapes but - when he found he couldn't stretch that far - decided they were sour anyway. So, a feeling of sour grapes is a pretended lack of desire. Thus, if it fitted the specific situation you are writing about, you might write: "The unsuccessful candidate pretended he had no desire for the post."
Ah! That's going quite a bit further than just 'sour grapes', I'd suggest, Bubbles. What's wrong with a phrase based on your own words, 'seek revenge'? Revenge, by definition, invariably implies a previous hurt, so that covers the scorning element.
if it was a sour grapes situation, the woman scorned wouldn't seek revenge, she'd just claim she never liked the guy anyway. So I'm not sure the phraise really applies here? Quizmonster's suggestion sounds sensible.