An Emo goes to the library...
An Emo goes to the library and asks the librarian, "Excuse me, do you have any books on suicide?". The librarian replies, "Well, we used to, but you idiots never bring them back!"
This is a joke which insults emos, calling them idiots. It also makes the implication that the reason why they never bring the books back is because they commit suicide, and then are unable to bring them back on account of them being dead.
That makes this an example of dark humor, or black humor.