When an atheist or agnostic tries to vihimently convince people to stop beliving in God (or religion in general). Whereas a Christion spreads the good news (evangelization) because he is happy and joyful, and wants others to share in his joy, dysangelization involves a depressed atheist or agnostic who thinks he knows everything (or is capable of knowing everything) about reality, and that this world is all there is, and wants everyone else to be depressed like him.