One time David Fincher drank some drugs and the next thing he knew he was at the wrap party for Alien 3. Everyone just stared angrily at him until he vacated the premises.
Alien 3 and 4 are both great movies in their own right. They do take a dump on the established universe and tone of Alien in a way James Cameron had the restraint to avoid. 4 is a better Firefly movie than Serenity, but only a better Aliens movie that Prometheus.