**Core Concept:**
Temporal arteritis is a rare inflammatory condition that affects the large arteries supplying blood to the head and neck, primarily the temporal artery. It is often associated with systemic inflammation in patients with an autoimmune disease called giant cell arteritis (GCA). Temporal arteritis can cause serious complications if left untreated due to its potential to lead to ischemic complications affecting the brain, eyes, and other vital structures.

**Why the Correct Answer is Right:**
The correct answer, "Headache," is the most specific symptom of temporal arteritis among the options provided. Headache is a presenting symptom in most cases and is often the only symptom in the early stages of the disease. This is due to the involvement of the temporal artery and the surrounding tissues, leading to ischemic pain and tension-type headache.

**Why Each Wrong Option is Incorrect:**
A. **Temporal Blepharitis:** Temporal blepharitis is an inflammation of the eyelids, not specifically related to temporal arteritis.
B. **Conjunctivitis:** Conjunctivitis refers to inflammation of the conjunctiva, which is not specific to temporal arteritis.
C. **Temporal Arteritis (incorrect term)**: Although temporal arteritis is the correct term for this condition, the question asks for the most specific symptom, and headache is the answer.
D. **Temporal Artery Bruit**: A temporal artery bruit refers to the audible pulsation of the temporal artery due to increased blood flow, which may be present but is not specific to temporal arteritis.

**Clinical Pearl:**
Giant cell arteritis (GCA) is often associated with other symptoms such as jaw claudication (pain on jaw opening), scalp tenderness, and temporal artery tenderness. However, headache remains the most specific symptom, and even in its absence, temporal arteritis should still be considered in older patients presenting with a new-onset headache, particularly when accompanied by other clinical findings mentioned above.

**Correct Answer:** Headache (Option D)