Phrase used to express disagreement or displeasement with a statement made by another person. It is used normally within discussions about video games on forums and imageboards.
The phrase originates from the relationship system that forms part of Bioware's title, Dragon Age: Origins, where the aforementioned Morrigan is found as an ally and playable character. This character is known for being quite good-looking, for her ability to shapeshift and for her bizarre opinions on pretty much everything, causing almost every attempt to start a conversation with she getting mad at you and the game displaying "Morrigan Dissaproves"
(general thread about first person shooters)
User 1: i think halo is teh best game evar!!!!1
User 2: Morrigan Disapproves
Morrigan: My mother and I spent good days killing the city wards.
Player: But is your mother a witch?
Morrigan: Oh, don't call her a witch, that is a very ugly word *morrigan disapproves*