Not every anime character is a mature, sophisticated person who makes decisions based on reason or a carefully thought out plan. Actually, some are the exact opposite - they're anime manchildren.
What is a manchild anime character? It's a character who may have been alive long enough to technically reach maturity, but emotionally speaking, they're nowhere close. These characters refuse to take personal responsibility for themselves, throw tantrums when things go wrong, and delight in childish pursuits like candy and toys. Combine this kind of behavior with the violent tendencies of a villain, and you have the 'psychopath manchild' - a truly dangerous character type who can't be trusted to behave rationally. Despite the name, these characters aren't all men - a few, like Toga Himiko of My Hero Academia, are actually women.
As you read, keep in mind that the term 'psychopath' isn't referring to any actual psychiatric conditions or personality disorders, or to any real human beings who might have those conditions. Here, it's just an interesting lens through which to view anime characters.
Himiko Toga is among the youngest members of the League of Villains, and she's also one of the least mature. She has very simple ambitions - to stab the people she likes and steal their blood so that she can become them. Despite the violent nature of her goals, she still expresses childish delight about them.
Gluttony is one of the homunculi created by Father to help him become a god. But just because he has a villainous purpose doesn't mean he's approaching it in a calm and mature manner. As his name suggests, Gluttony makes most of his decisions with his stomach - and those that he doesn't are made by his desire to win Lust's approval.
Mad Pierrot is an unstoppable force of destruction who is largely bulletproof and unable to feel pain, and finds great amusement in the agony of others. Though he's usually laughing and having a good time, when he actually does experience pain, his psyche is destroyed. He didn't get this way by accident - he's actually the victim of human experimentation designed to create a super-soldier.
Beerus is the god of destruction, and his machinations are crucial for the overall survival of the universe. However, some of his behaviors don't seem to line up with his stated goals. He chooses what to destroy based on whether or not he can get delicious food out of it, and he gives up on his goals out of boredom or because he wants to take a nap.