In Dungeons and Dragons, we tend to face a lot of bumps in the road from both the Player and DM’s end. This is normal, however it is also an inconvenience to all those in the game. Cases such as DM’s going out of their way to kill players and players knowing where some things are located and the stats of enemies.
DM empowerment sometimes gets abused. Throwing creatures of overbearing power to players who are weak in comparison for the purpose of killing the party. Another sample would be the DM going completely against a single player in order to counter their build or such. Both scenarios are not fun for the side of the players.
DM’s must remember that they are the Narrator of the story and not the villain of it; sure you play the villain of the story, but that does not mean that you are the villain. DM’s must learn to distance themselves from the characters they put into the story. Sometimes you fall in love with your villains that you would do underhanded things from an OOC perspective to keep them alive. That is not what the game is about. When roleplaying these NPC’s, play them as their personalities would have them. A few tweaks in order to keep them fun and all would be fine as well; but remember that the heroes of the story are the players and that you are the storyteller.
Some players create builds which are completely overwhelming for new and even some veteran DM’s, there are a few on the opposite side of the spectrum which create underwhelming builds which don’t do much to contribute; others would create builds which could “see” the stats of the enemy monsters, others would just use their OOC knowledge against these monsters. Now, not all players are like this, but there are a few in the community that we know who are like this. All of the examples used drain the fun from the game for everyone except the user, usually at least.
Now remember, there is no such thing as “Wrong” fun. Every type of fun is fun for certain people; however, for those who prioritize their fun over the fun of others, please be considerate. Everyone plays the game for fun. Sure people enjoy the crazy, powerful, nonsensical builds out there, but one has to make sure that they also share the spotlight with other players so that everyone on the table would have a pleasant time; the same goes for those with cooky builds as well.