**Core Concept**
The "cayenne-pepper" appearance on diascopy is a characteristic dermatoscopic finding associated with a specific condition. This phenomenon is observed when a special type of blood vessel is compressed against the skin surface, resulting in a distinctive appearance.

**Why the Correct Answer is Right**
The correct answer is related to a type of vascular anomaly. The "cayenne-pepper" appearance is a classic sign of **Kaposi's sarcoma**, a rare cancer that affects blood vessels. When a dermatoscope is pressed against the skin (diascopy), the characteristic pattern of dilated, tortuous vessels is revealed, resembling the appearance of cayenne pepper. This is due to the abnormal proliferation of spindle cells within the vessel walls, leading to their dilation and tortuosity.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it doesn't relate to a vascular anomaly or a condition that would produce a "cayenne-pepper" appearance on diascopy.
* **Option B:** This option is incorrect because it's a different type of skin lesion that doesn't typically present with a "cayenne-pepper" appearance on diascopy.
* **Option D:** This option is incorrect because it's a condition that affects the skin but doesn't typically produce the characteristic vascular pattern seen in Kaposi's sarcoma.

**Clinical Pearl / High-Yield Fact**
Kaposi's sarcoma is a type of cancer that's associated with immunosuppression, particularly in patients with HIV/AIDS. The "cayenne-pepper" appearance on diascopy is a key diagnostic feature of this condition, and dermatologists often use this finding to make a rapid diagnosis.

**Correct Answer: C. Kaposi's sarcoma**