Software developers who never have, and never will have to, use the software for real. I think every coder should be forced to use their own software for one month out of every year they work on it (and be able to do the job that goes with it because how the fuck else are they going to get a clue?).
And fucking stop making PC software that looks like it was designed to be used on a phone. I cannot do my job on a phone, no one would ever do my job on a phone, everyone who does my job has at least two large screens. We do not want to click a million times to do one simple task, and we do want to be able to see masses of information at the same time.