Having a co-worker who I consistently must support with using the basic funionaity of our software, getting me dragged in to a senior management meeting to tell me and my boss that I am too incompetent to do my job. All because something out of my control was taking longer than they would have liked.

This same co-worker deleted a folder on a server full of live data because they "wanted to see what it would do" then wondered why I revoked their Admin rights to that folder.

I want to scream at them every day.