This one is more Albus-centric. He has so many layers, doesn't he?
~Multi-Faceted~
IV: Wrath
By nature Albus Dumbledore was a calm, patient, forgiving man. It was difficult to unsettle or anger him; this only doubled in difficulty when contact with Harry further mellowed him out. Short of Lord Voldemort and his Death Eaters, even Severus Snape could not easily irritate him, let alone make him give in to the pull of unleashing the Elder Wand's considerable power.
That all changed when anyone meant Harry harm.
People would be stunned to know that the kindly, eccentric, passive headmaster in him became an enraged, protective bottle of power when someone hurt Harry James Potter. He lost all semblances of patience and dignity, became so dangerously furious that even Voldemort would wet his pants if he had any decency left in him.
The Elder Wand usually came out then, and did its horribly dirty work in the name of (of all things!) protection and love.
Later on Albus would laugh, self-consciously, at how impassioned he could be in the heat of the moment.
But only later. Harry was his own, and anyone trying to end that bond was a serious threat - and, in the end, usually wished that they had never crossed Hogwarts' greatest headmaster.