In our Monday / Wednesday class, we're still debating the difference between "sour" and "bitter". But have you heard the expression, "sour grapes"? We use it to refer to a person's attitude when they pretend to despise something because they cannot have it themselves. Look:
A: "Well, perhaps a ferrari isn't such a fantastic car."
B: "That sounds like sour grapes to me."
The origin of the phrase comes from one of Aesop's fables, The Fox and The Grapes. It's also the title of a collection of early poems by the American physician and poet, William Carlos Williams. For other expressions with "sour", click here. For a curious use of "bitter" as a noun, click here.