It's a way of showing that you are
not interested in someone's opinion or what
s/he said does not
appeal to you at that particular moment.The one who says this uses a rather sarcastic tone to express his/her disinterest in the topic.
Faddy: Hey,I just saw Avatar on 3D....it was awesome!
Gabby (really doesn't give a damn about the movie):
Ah ok! What time is it right now?
Faddy: Dude,you are
not interested,that's not cool,you are changing the topic now.
