Adam is sush a good villain, he is one of my favorite, he is a toxic misogynistic douchebag that you have fun love to hate. He's funny and entertaining. He's complete opposite of Charlie. Charlie is a demon in hell, but as person she's a true angel who committed all 7 virtues in first episode, when Adam is an angel in heaven, but as person he's true demon who committed all 7 deadly sins in the same episode. Charlie's trying to solve the problem of overpopulation of sinners by the idea of redeeming them, so basically pacifist route, when Adam's idea is exterminating sinners, genocide route. And when the main guestion, why Adam is an asshole and in heaven? Note to the beginning when Lucifer gave Eve fruit of knowledge (where's popular theory that after Eve ate apple, Root of all Evil took over her body and became a character named Roo, a future antagonist). So, when Eve ate apple, Adam is nowhere to be seen. So basically in hazbin hotel universe, Adam didn't ate apple. Do you know what it means? So basically Adam is a child in grown man's body who doesn't have any knowledge about morals, what's right or wrong, the difference between good and evil. He get to heaven (in ep 6 and 8 we learn that angels don't choose which soul get to heaven or hell, they get automatically). Higher angels acceptd him as one of their own, thinking that if he's in heaven, that means he's good flawles person and everything what's he's doing is ok and they don't argue with him. They teach him black and white rules. Angels in heaven are good, sinners in hell are evil. Just because he's a first human soul in heaven they give him higher status,labeled him as someone so special and significant important, fed him a story as flawless man and progenitor of mankind and the fact that he's he had a life with no normal discipline and punishment, not facing a consequences of his own actions, not learning from his mistakes. So basically Adam get corrupted by all this and doing whatever he wants for his own entertainment and also maintains his importance in heaven, and he became spoiled frat bro with God complex. He swears a lot because again, he is a big extremely immature child who didn't normally grow up in heaven, so basically he as child thinks that swearing is cool and angels don't argue with him about that.