Situation #1: Everybody assumes that someone else will do the right thing, but no one does, and so the right thing is never done. EXAMPLE: A crowd of people watch as a person is maliciously assaulted. Everyone assumes that someone else will call the police (or otherwise intervene), but no one does, and the assault continues.
Situation #2: Everybody assumes that everyone else will do the wrong thing, so they might as well do it, too, and no one does the right thing. EXAMPLE: My city begins using buses in order to ease traffic congestion. However, since buses travel on city streets and are thus susceptible to the same problems as private cars (traffic congestion, stop lights, etc.), I might as well drive my car. [Everybody assumes this and thus traffic remains just as bad.]
Situation 1: The Bystander Effect, Diffusion of Responsibility
Situation 2: (Seems to be) Diffusion of Responsibility
The Bystander Effect = The greater the number of bystanders who witness an emergency, the less likely it is that one of them will help
Diffusion of Responsibility = Each bystander’s perception of their responsibility to help decreases as the number of witnesses increases. No one feels that it is their personal responsibility to take action.
It seems to me that the above is more of a game-theoretic phenomenon than a psychological problem, since the participants may very well be assessing the situation accurately and behaving rationally. I would call it a collective action problem.