When a character expresses a moment of joy in the most deadpan manner possible. Often by saying the word "yay" or "woo hoo" in a flat monotone or other tone of voice that does not exhibit joy.
Can frequently be used sarcastically, when the "joy" is invoked by something very much not joyful. In this circumstance, it is inevitably said by the Deadpan Snarker. Just as often, however, the character [...] [tvtropes.org]