Stupidity: The Nostromo essentially is a detachable ship attached to a mining platform. After it returns and docks with the platform, much of the movie occurs in the platform section and not the Nostromo itself. The supposed reason they can't just blow up the ship is that the shuttle can't fit everyone. Why couldn't they just lure the alien into the platform, seal the ship, and then use the ship itself to escape? They could then blow up the platform to kill the alien.
Stupidity: After Corinne Dufour realises that Drax intends to have his dogs kill her, she inexplicably attempts to flee on foot, running right past the golf cart she arrived in. The golf cart would have given her more speed, range and protection, and would have been a much better choice for fleeing.
Suggested correction: Golf carts are very slow, and are open on all sides: the dobermans would've easily dragged her off it. The biggest stupidity here is that she should've fled to a crowded area with other people instead of the woods. Then again, she was panicking, and not thinking straight.