I'll never forget the time I failed to learn an important school/job skill:  Interpolation, which is a fairly simple mathematical operation to get a specific value from a table of numbers.  I was in class in college, and the professor said something about using interpolation to find a number.  One of the students raised their hand and asked him to explain.  He responded, "You know what interpolation is.  I'm not going over it."  And that was that.  Several students complained, but the professor just moved on without teaching it.  The concept itself isn't all that complicated, and it can be taught pretty easily, especially to engineering students who are already well-versed in math.  I ended up learning it on my own and still use it today on a very regular basis.  I still can't believe I had the privilege of paying to not learn something. 

It happened again another time in college, when I first encountered the concept of a hyperbolic trigonometric function.  It happened the same way, with the professor casually breezing through a part of a problem that had to do with hyperbolic functions.  I'd heard of them before, but had no real idea how to use them or what they were for, and several people in class agreed with my ignorance.  The professor said something along the lines of, "You should already know that," and simply moved on.  To this day, I still have no idea what a hyperbolic function is or what it can possibly be used for, and not only do I not care, I firmly blame that educator for my lack of knowledge. #education