I didn't do anything special at all, one day he stopped running when he saw me, then a whlile later he started flaring his gills and aggressively wagging his tail when I approached.
I like to tease him, quickly moving my head from one side of the tank to the other, he chases me furiously and sometimes even bites the glass.
That's only within the last couple of months he's started to bite the glass.
Funny thing is, he's slightly less aggressive with other fish than he used to be. He doesn't kill them instantly anymore.