**Core Concept**
The patient's presentation of sudden onset severe headache, vomiting, neck rigidity, and the absence of focal neurological deficits is suggestive of a non-atherosclerotic, non-inflammatory cause of subarachnoid hemorrhage (SAH). This condition is often associated with the rupture of an aneurysm or arteriovenous malformation (AVM) in the brain.

**Why the Correct Answer is Right**
The sudden onset of severe headache, often described as "the worst headache of my life," is a classic symptom of SAH. The headache is usually accompanied by vomiting and neck rigidity due to irritation of the meninges. The absence of focal neurological deficits indicates that the SAH is not causing significant brain tissue damage. The likely cause of SAH in this patient is the rupture of an aneurysm or AVM, which can lead to bleeding into the subarachnoid space.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because SAH is not typically associated with atherosclerosis, which is a risk factor for ischemic stroke rather than SAH.
**Option B:** This option is incorrect because inflammatory causes of SAH, such as meningitis or encephalitis, typically present with fever, altered mental status, and focal neurological deficits.
**Option C:** This option is incorrect because vasculitis is a rare cause of SAH and typically presents with systemic symptoms such as fever, weight loss, and skin rash.

**Clinical Pearl / High-Yield Fact**
A key feature of SAH is the presence of "Thunderclap headache," which is a severe headache that reaches its maximum intensity within 1 minute. This type of headache is often described as "the worst headache of my life" and is a classic symptom of SAH.

**Correct Answer:** D.