This is an emotion John knows all about. He feels it coming before it starts, the bubble of rage deep within him, born of a desperate, futile, urge to protect what has already been lost.
He wants to strangle Mycroft until that smug look vanishes.
He wants to kill Moriarty slowly, to make him feel every inch of it.
He wants everyone responsible in any way to suffer and die, and that includes himself, because he wasn't fast enough, strong enough, good enough to save Sherlock. He didn't say the right things, didn't catch the signs.
He'd start with himself.