Seems most are going for options that amount to abuse of power whilst in the public eye. I'd be more inclined to err towards abuse of power when behind closed doors, without any perks other than satisfying cruel perversions on offer.
I can sympathise with the perils of weighing up complicated cause and effect scenarios. Sometimes people end up doing bad things for good reasons, bad things to the few for the sake of the many. I can even sympathise to an extent with those that succumb to the temptation of viewing the people they rule over as nameless and faceless pawns, ripe for the using for the leader's own gain.
What I can't get past, or comprehend, is how an adult could wield power over a child, very much with a face and a name - also with what would have been a bright future but for the adult extracting fleeting pleasure from the child, and it's rightful proper chance at life in the process. If courage is being scared but doing it anyway, then for me the worst humans are those that when faced with uncomplicated decisions, with dire consequences for another or others, and with nothing of substance to be gained, proceed to do it anyway.
I doubt I'll ever know which one the particular worst abuser is. I assume that their abuse of power would be far too effective to allow knowledge of them. Knowing and imagining the depths of human behaviour, I doubt I'll be putting forward an actual name at any point.