I found with mine (over a 2-3yr period) that as long as nothing tried to square up to him, he was fine, and in fact peaceful....... "walked quietly and carreid a big stick".
So long as he was allowed to be the first to feed, and so long as others basically moved out of his way, then he was fine...... if something did challange him, try to feed before him, or was stubborn and did not give him a wide birth, then he would chase them up and dwon the tank once or twice to emind them who was boss, and then all would be rosy again.
I would certainly say he was not a bully, and did not chase other fish for chasing sake, or nip at the others fins or anything, just for the hell of it - the way say a damsel would.
But by all accounts they are a very variable fish..........
HTH
Matt