A group of my friends and I have started d&d campaign, None of us are experienced in d&d, so this is mostly our first time playing it. It started out pretty fun, but one of the players has become a bit of a problem. During character creation, he chose an incredibly overpowered homebrew class, making him about as effective as the rest of us combined. Because of this, he's started acting like the groups leader, by making sure to be the first to act in almost all scenarios, even cutting other players off to do so, and since his character is evil, his first action tends to be attacking whatever we encounter, regardless of whether or not the DM wants us to handle the situation diplomatically. He's also hoarded over half the teams magic items, which has only lead him to become even more powerful. The DM's been trying to fix this, by suggesting a class change, but the player mostly refuses to admit the character is too strong, and will often argue with the DM about how some of his abilities work. Lately, the DM's tried to put more pressure on his character by having enemies focus him more, or putting him in more difficult out of combat situations, but this has only made him argue with the DM more. I'm sorry if I'm whining too much, but this is seriously taking the fun out of the game, and I don't know what to do. The player is a good friend of mine, but I know that he doesn't take direct criticism very well, so I don't want to flat out tell him that he's playing annoyingly, but I can't think of anything else. If you could suggest anything, it would be greatly appreciated.