Used to express disgust, distaste and being generally fed-up with something in particular, or simply the world in general. The level of emphasis given to the word is an indication of how stongly annoyed the speaker is.
Tutor: Can you get this piece of work done by Friday instead of Monday?
Pupil: Of course.
Pupil (inwardly, or later, to friend): Meh, where am I supposed to find the time to do that?