Frustration for a sysadmin (well, for me)
To amplify on a previous entry, I've found that the biggest thing that gets under my skin as a sysadmin, that really leaves me frustrated and short-tempered, is being helpless. Well, not exactly helpless in general; what I mean is being faced with a situation where there's a technical problem (something within my sphere) but there is nothing that I can do, or nothing useful (where I know I am just flailing around, taking random stabs completely in the dark).
This might seem counterintuitive to outsiders, because sysadmins spend a lot of time troubleshooting problems; if doing this frustrated me that much, you'd think that I'd have gotten into a less annoying field by now. But even with apparently mysterious system problems there are usually a lot of things that we can do to diagnose things and to move forward, to at least get closer to a solution; we have piles of tools and techniques and so on. Even if we're not solving the problem right now, we're productively working on it.
(Well, in theory. In practice it can be both tedious and mysterious to try to run down a problem as you diagnose just what's going on; I have spent more than enough time waiting for test runs to finish and the like.)
However, every so often these tools and techniques run out, or I'm stuck in a situation where they're not available; then there's no feeling of productive work, no forward motion on the problem, no nothing, and I am sitting there helpless and powerless. That's when it all gets to me, sometimes badly.
(My classic weak spot is trying to make various sorts of serial connections work; there are so many different things to go wrong, and basically no troubleshooting tools.)