The one thing that I absolutely can't deal with is trying to bat clean up for people who really fuck up or don't know what they're doing. There's one project at work that is pretty much always that scenario. Generally it's the responsibility of one of the developers, but he's sick. So I'm trying to decipher what the fuck is going on and I can't tell.
This is the only thing that I ever encounter in my professional life that pushes me to the edge. I don't have the patience for it. When you add up a combination of things that make it hard to professionally debug a problem (little things like source control, documentation and the right tools), it's like beating your head up against the wall. And frankly I don't like the pain.