meh

Used when one is happy, sad, excited, etc.
Usually used when one is irritated, however.

It is becoming quite a common occurance in the vocabulary of Western Pennsylvanian school students.

Student 1: "You're such a bitch, Haley."
Student 2: "MEH, Caitrin. Mehhhhh."

or

Boyfriend: "Melissa, this just isn't working out."
Girlfriend: "But..But...MEHHH="