An evil person isn't usually going to tell everybody they are evil, since that wouldn't get them too far. More of the good life goes with claiming to be a good, honest, or trustworthy person, and if suspicion is deferred to others long enough, people will usually quit questioning what the evil person is really like, they assume the person is good by nature.
If people people told you that they were evil in plain language, nothing would be left to question.
An evil person isn't usually going to tell everybody they are evil, since that wouldn't get them too far. More of the good life goes with claiming to be a good, honest, or trustworthy person, and if suspicion is deferred to others long enough, people will usually quit questioning what the evil person is really like, they assume the person is good by nature.
If people people told everybody that they were evil in plain language, nothing would be left to question. Usually they tell everybody else (the public) something different than they tell you behind the scenes, when nobody is looking.
Evil people don't turn evil, they just wear a good humanitarian facade (though not every humanitarian is superficial or evil, it's just a good place to hide in plain sight for those that are, among people the word thinks of as wonderful) in public, they try and light up the world with talk and preaching about equality, desegregation, justice, and things that sound good to a broad audience rather than a narrow, exclusive one (Hitler did the same thing by talking about peace and prosperity), but their true nature isn't as broadly known, as only a few people know about isolated incidents from the past that they found disturbing about the evil person (almost invisible from the outside observer).
He/she had always been evil and sleazy, even as a kid, but most of his/her audience didn't actually know much about his/her life or past beyond the public facade, the face the community at large saw most of the time, the one they thought was the real version of them.
Something that doesn't show up on a lie detector or psychological exam. A mass murderer or serial killer doesn't tend to provide much foreshadowing of what he/she will do in a few decades, or what will lead up to it, even though people always try to go back and study or research the person's behavior, or ask people that knew them if they remember anything about the person. There's not really a simpler explanation than the person was always evil below the surface, no matter how good or humanitarian (or charitable/warm/generous) they seemed on the surface. Evil people can smile just like anybody else can.
The evil guy/girl knew that hiding in the light where everybody could see him/her would keep him/her in business longer than hiding in a dark alleyway where everybody would think to look for evil and creepy people/shit.
Just like an addict isn't going to put a neon sign to let an officer know where they congregate so that they can come and arrest them (even if everybody knows already) , an evil person isn't going to wear a neon vest saying BAD PERSON COMING THROUGH WEARING BOMB ON VEST, A LOT OF PEOPLE WILL DIE BECAUSE OF ME, STAY BACK, or hide in a dark alleywayway most of the time, somewhere that would draw suspicion that couldn't be readily deferred quickly (some might be found in an alleyway, but it's not as likely as somewhere less obvious, since an evil person wouldn't benefit much from staying in an alleyway for an extended amount of time).
Most evil people prefer to make themselves look wonderful, not evil. Once people know somebody is evil, they start to lose credibility for anything they did that people thought was good or positive, even if there intentions or nature never was good any any point in their life, and the acts people thought were good were really a way to mask their true nature.
Someone who drinks both Pepsi and Coke
"Eww, look at her. She's drinking Pepsi AND Coke. She's evil.
A word to describe the emptiness of love
I am evil! -Mcevilian Evilstein