Sending a paper you're really excited about to a teacher you really respect and admire, and hearing back that she thinks it's awful. Not that it "needs work"; not full of hard-nosed but ultimately helpful suggestions for improvement. Simply, telling you that it is an abysmal piece of work and she hopes you never tell anyone she had anything to do with you misguided attempt to "inflict" your writing on the subject.*
I'm not blaming anyone -- maybe the paper deserved it. But it's still definitely falls into the category of things that suck.
* A quick addendum. Obviously, part of this is that this person is no longer my teacher, and thus no longer has any obligation to help me "improve" an idea she thinks is just plain bad. That's a shift in role that undoubtedly take some getting used to (by me, not her) -- though it's not like I was totally unaware of it while I was reading her comments. So again, the point isn't to lash out; nothing "wrong" happened here. But that doesn't make it any easier to hear, no?