one of my boys couldnt be bothered anymore(he's sort of an old man at this point...very laid back).
my second boy is sort of scared by his reflection. flares and darts around like a maniac!!!
my third boy flares at anything and everything. sometimes its the snail...sometimes its me....sometimes it is a plant...sometimes it is the bubbles from his sponge filter...rocks...food...and sometimes he just does it for seemingly no reason(to show iff i think)...i guess it gives him a fun activity as he sees it.
they all are so different that yes, i chalk it up to individual personality.