As was mentioned in the previous post, a pacifist is a person who is opposed to war or violence of any kind. Throughout the novel, Holden Caulfield is not a pacifist. In Chapter 6, Holden is upset at his roommate Stradlater for withholding information about his date with Jane Gallagher. Holden cannot control his temper and attempts to punch Stradlater in the face but misses. Stradlater ends up pinning Holden on the ground, and Holden begins to insult him. Stradlater warns Holden several times to stop insulting him, but Holden continues to harass Stradlater by calling him a moron. Stradlater then punches Holden in the nose. After the fight, Holden says that he is not too tough and considers himself to be a pacifist.
This comment is typical of Holden Caulfield. Holden is an unreliable narrator whose perception does not match reality. Holden expresses his anger by taking a swing at his roommate, then continues to insult Stradlater which amplifies the situation. Throughout the novel, Holden continually gets himself into altercations by aggressively insulting others. Although he does not always physically fight, Holden uses his words as weapons and is a controversial individual. Holden also fantasizes about war and mentions that the only reason he is opposed to joining the Army is because he would have to spend all day with guys like Ackley, Stradlater, and Maurice. Holden does not possess deep convictions about how he is opposed to war, fighting, and violence which is why he is not a pacifist.
A pacifist is a person who avoids conflict and opposes violence as a means of settling a dispute. It depends on your interpretation of the novel and what Holden says as to whether you believe he's a pacifist.
Remember that Holden in an unreliable narrator--he admits he's a terrific liar. In one breath, he says that he's a pacifist, and, in another breath, he says he's a sadist (someone who enjoys inflicting pain on others). The only real act of physical violence Holden commits in the novel is attacking Stradlater, which doesn't work out too well for Holden, possibly indicating that Holden doesn't have much experience with violence.
When Maurice and Sunny return to Holden's hotel room in New York, Maurice continues to physical assault Holden, and Holden does little, if anything, back to him. Also, based on what Holden tells us about his emotional state, there have been plenty of opportunities for him to get violent, and he hasn't.
I think Holden is more of a pacifist than a sadist, but not on purpose. Holden doesn't mind seeing other people hurt--he's usually not the cause though. Holden also doesn't seem morally opposed to violence; it's just not his style.