The antonyms for the phrase "show courtesy" are quite varied and often depend upon the context in which the phrase is being used. One common antonym for the phrase is "show discourtesy," which refers to behavior that is rude, disrespectful, or impolite. Other antonyms for "show courtesy" may include actions or behaviors that are indifferent, impolite, thoughtless, or inconsiderate. In some cases, the opposite of showing courtesy may be to ignore or neglect someone, to treat them unfairly or with hostility, or simply to be unresponsive. Ultimately, the antonyms for "show courtesy" are a reminder of the importance of treating others with kindness, respect, and consideration, even in the face of difficult situations.