**Core Concept**
Passive-aggressive behavior is a defense mechanism characterized by indirect, often subtle, expression of negative feelings, such as anger or resentment, through actions rather than direct communication. This behavior is typically seen in individuals who struggle with expressing their emotions openly, leading to a sense of control and avoidance of confrontation.

**Why the Correct Answer is Right**
In this scenario, the son is exhibiting passive-aggressive behavior by dropping the glass, which can be seen as an indirect expression of his reluctance to comply with his father's request. This behavior allows the son to act out his negative feelings without directly confronting his father. This mechanism is often used by individuals who feel powerless or trapped in a situation, as it provides a way to express their emotions without being held accountable for the consequences.

**Why Each Wrong Option is Incorrect**
**Option A:** Reaction formation is a defense mechanism where an individual adopts the opposite behavior of what they truly feel, often to avoid anxiety or conflict. In this case, the son's behavior is not an attempt to adopt a behavior opposite to his reluctance, but rather an indirect expression of it.

**Option B:** Denial is a defense mechanism where an individual refuses to acknowledge or accept an uncomfortable reality. In this scenario, the son is not denying the request, but rather expressing his reluctance through action.

**Option D:** Acting out is a term often used to describe behavior that is a direct expression of an individual's emotions, often without consideration for the consequences. In this case, the son's behavior is not a direct expression of his emotions, but rather an indirect one.

**Clinical Pearl / High-Yield Fact**
Passive-aggressive behavior can be a challenging defense mechanism to address in therapy, as it often requires the individual to confront and express their emotions openly, which can be uncomfortable and anxiety-provoking.

**✓ Correct Answer: C. Passive aggression**