Those who say they can't use built-in functions but when pressed and asked why, and if it's homework, will go to extraordinary lengths to avoid disclosing that it's homework.
Those who, after being provided with simple demos they can adapt, say they're beginners and can't do it, and can I do it for them.
Those who accept the shortest answer, not the best answer because they think a longer self explanatory solution with descriptive variable names, lots of comments, and graphs and figures to show results, just looks too complicated, even if the shorter solution they accepted is more cryptic for beginners (like it uses anonymous functions, cellfun(), bsxfun(), arrayfun(), regular expressions, etc.) and they have to come back and ask for an explanation of it.
Those obsessed with getting a fast solution who blow right past the posting guidelines, which leads to several back and forth clarifying questions from us to get the info they should have posted in the first place if they had just read the posting guidelines. Contrary to what they think, this actually makes it take longer for them to get a working solution.
Those who won't post code or data, despite being repeatedly asked directly. They are obsessed with the idea that we should be able to read their mind and give the solution after having seen only a snippet of their code.
Hopefully no one will think that we are "mean" because we're posting these (like this poster). After all, we just want to provide them the best solution in the fastest amount of time, with the least effort by us.