**Core Concept**
The pathognomonic sign of irreversible cell injury refers to a specific cellular alteration that indicates a cell has crossed the threshold from reversible to irreversible damage. This concept is crucial in understanding cell death mechanisms and their implications in various diseases.

**Why the Correct Answer is Right**
The most pathognomonic sign of irreversible cell injury is the disruption of the plasma membrane's integrity, leading to the loss of cellular contents. This disruption is characterized by the formation of blebs and the breakdown of the cytoskeleton, resulting in the cell's inability to maintain its shape and function. The loss of membrane integrity is often associated with the activation of various cellular enzymes, including lysosomal enzymes and proteases, which further contribute to cellular damage.

**Why Each Wrong Option is Incorrect**
**Option A:** The swelling of cells, or hydropic change, can be a feature of reversible cell injury, making it an incorrect answer. While swelling is a common response to cellular stress, it does not necessarily indicate irreversible damage.
**Option B:** The presence of apoptotic bodies is a feature of programmed cell death, which is a distinct process from irreversible cell injury. Apoptosis can be a reversible process, and the presence of apoptotic bodies does not necessarily indicate irreversible damage.
**Option C:** The accumulation of lipofuscin is a feature of aging and cellular wear and tear, but it is not a pathognomonic sign of irreversible cell injury.

**Clinical Pearl / High-Yield Fact**
The loss of plasma membrane integrity is a critical step in the progression of cell injury, and it is often accompanied by the release of cellular contents, including enzymes and other biomolecules. This process can have significant implications for cellular function and the progression of disease.

**Correct Answer: C. Accumulation of lipofuscin is a feature of aging and cellular wear and tear, but it does not indicate irreversible cell injury.**