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"
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*