People who ask for help with XYZ and then it turns out that they haven't even started with ABC.
I've taken a lot of statistics classes in graduate school and taught myself how to use a specialized statistical software. I have a few friends who are graduate students in other departments who don't have the same statistical requirements for their programs, but for the most part they realize how helpful it is to know how to analyze their own data.
A few months ago, I helped friend Anna make her graph "prettier:" how to select particular colors and line types in plots and how to get everything perfectly aligned and labeled. It took me 30 minutes. Friend Betty thought that was great and asked for references for how to use that software so I sent her the PDFs of the books I taught myself with.
Thursday night Betty asked for help to make her own graph pretty. I offered to meet her first thing on Friday morning. Except she didn't even have the software installed, much less know how to use it. After getting that up and running, she had no idea of what she how she wanted to analyze her data. I suggested a few tests, but told her she needed to go back and discuss this with her major professor. At this point, it's been 3 hours of my time.
Saturday, she asks if she can stop by my lab for a few minutes with one or two questions. An hour later it becomes obvious that her data is incredibly flawed so I told her she needed to go fix her dataset.
Today, she asked if she could join my usual Sunday afternoon study group and ask a question or two along the way. Who wants to guess that she expected me to talk her through it step by step? I told her that I had my own stuff to work on and that a few questions did not mean that she got my undivided attention for two more hours.
Now Betty is upset because I helped Anna make a pretty graph but I wouldn't help her.