**Core Concept**
The question is testing the interaction between a specific oral hypoglycemic medication and alcohol, leading to a common side effect known as flushing. This phenomenon is related to the metabolism of the medication and its interaction with alcohol in the liver, resulting in the production of acetaldehyde, a toxic compound that causes vasodilation and flushing.

**Why the Correct Answer is Right**
The correct answer is **C. Tolbutamide**. Tolbutamide is a first-generation sulfonylurea, a class of oral hypoglycemic medications that work by stimulating insulin release from the pancreatic beta cells. When tolbutamide is taken with alcohol, it is metabolized by the liver enzyme aldehyde dehydrogenase (ALDH2), which is responsible for converting acetaldehyde to acetate. However, many individuals of East Asian descent have a genetic deficiency in ALDH2, leading to an accumulation of acetaldehyde and subsequent flushing.

**Why Each Wrong Option is Incorrect**
* **Option A:** Metformin is a biguanide that works by decreasing hepatic glucose production and increasing insulin sensitivity. It does not cause flushing when taken with alcohol.
* **Option B:** Glyburide is a second-generation sulfonylurea that also stimulates insulin release. However, it is not commonly associated with flushing when taken with alcohol.
* **Option D:** Pioglitazone is a thiazolidinedione that works by increasing insulin sensitivity. It does not cause flushing when taken with alcohol.

**Clinical Pearl / High-Yield Fact**
When prescribing oral hypoglycemic medications to patients, it is essential to consider their potential interactions with alcohol and other medications, as well as their genetic predispositions to certain side effects.

**Correct Answer: C. Tolbutamide**