Disorganized coworkers and coworkers who say they want more responsibility but won't do the groundwork.
I'm in the middle of planning a massive event. A coworker wanted to learn how to do the work I do, so our boss said, "Anon, support her doing this event and let her be the face of everything". 2 months ago, this seemed like a great idea.
Fast forward to now, 3 weeks away from the event, it's looking like a massive mistake. She has had several breakdowns and said "I can't do this", I've had to pretty much start from scratch to undo everything she's done and now the client is pissed at our entire team. If this were the first time this happened, cool, but it's really starting to wear me down.