DM improvement

What are the worst things a DM can do?

Let's make a list of the 10 sins of the DM, for the board's sake.

Write a "plot" for their campaign.

Get attached to an NPC. Or insert their waifu or similar as an NPC.

Offhand I'd say allow whiny fucks like you in their campaigns.

I did this. My PCs immediately killed him. Never again.

Lack luster caring for description .... it doesn't have to be overly detailed, and a picture is fine too.

... let's start and see how this is going
Thou shalt not write a "plot" for thy campaign
Thou shalt not get attached to an NPC and waifu insert.
Thou shalt not allow whiny fucks
Thou shalt not have lack luster caring for description

And then again some players require the railroad.

Disregarding his type of players is a better one.

Thinking the rules don't matter.

I mean choosing not to play with idiots is a prerequisite when playing any game, I don't think it needs to be written into the rules any more than "don't play with cheaters" needs to be explicitly written in the Monopoly rules.