Final answer:
The term 'boorish' refers to rough and bad-mannered behavior. In the context of the question, the correct answer is (c) Rude, as it aligns with the negative connotation of being boorish, while the other options suggest polite behavior.
Step-by-step explanation:
The word boorish describes behavior that is rough and bad-mannered; therefore, the option that defines unexpectedly boorish behavior toward others is (c) Rude.
The excerpt suggests that the speaker felt slighted by the behavior of another, indicating that there was a sense of disregard or potential rudeness in their interaction. Describing someone's behavior as cold, condescending, or critical can also carry connotations of rudeness, depending on the context.
In this case, other options such as cordial, polite, and gracious do not align with the meaning of boorish, as they all describe pleasant and respectful behavior, which is the antithesis of being rude.