**Core Concept**
Gastric outlet obstruction is a mechanical blockage of the gastric outlet, typically resulting from a peptic ulcer that has penetrated the muscularis propria and eroded into nearby structures, leading to fibrosis and scarring. The pylorus, a region of the stomach, is the most common site of obstruction in gastric outlet obstruction.

**Why the Correct Answer is Right**
The most common site of obstruction in gastric outlet obstruction is the pylorus, where the antrum of the stomach meets the duodenum. This is due to the fact that peptic ulcers often occur in the antrum and can erode into the pyloric channel, leading to fibrosis and scarring, which can cause obstruction. The pyloric channel is a narrow passageway through which gastric contents flow into the duodenum, and any narrowing or obstruction of this channel can lead to gastric outlet obstruction.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the gastroesophageal junction is not a common site of obstruction in gastric outlet obstruction.
**Option B:** This option is incorrect because the distal ileum is not a common site of obstruction in gastric outlet obstruction.
**Option C:** This option is incorrect because the jejunum is not a common site of obstruction in gastric outlet obstruction.

**Clinical Pearl / High-Yield Fact**
It's essential to note that gastric outlet obstruction is a medical emergency and requires prompt diagnosis and treatment to prevent complications such as malnutrition, dehydration, and electrolyte imbalances.

**Correct Answer:** C.