Greetings Jura :) Sour grape is a communication that belittles somebody or something ,sort of a belittling comment. It usually is a sign of lack of respect by patronizing the receiver and doing that specifically with things that are unattainable: In the fable The Fox and the Grapes, which is attributed to the ancient Greek writer Aesop, the fox isn't able to reach the grapes and declares them to be sour - "the grapes are probably sour anyway!". The dictionary states it also as : "a false accusation of an offense or a malicious misrepresentation of someone's words or actions".

In short sour grapes means disparagement of something that is unattainable.

haha,interesting，that we have same thing in chinese."when you say they are sour grapes is because you canot get the grapes."吃不到葡萄说葡萄酸。^_^

it means the grapes are not yet ripe, and you got cheated into buying them haha!