Situation #1:

A teammate makes an off-color joke (e.g. involving an offensive stereotype) at a project meeting.

Situation #2:

A fellow graduate student receives a public dressing down by a professor in a lab meeting.

Situation #3:

In a small-to-medium-sized class you see another student repeatedly surfing the net on a laptop. It's distracting. The instructor has not said anything.

Situation #4:

You hear a fan at an athletic event make a cruel remark about someone on the opposing team, who seemed to overhear it.

Situation #5:

One person in your lab or group frequently makes critical or even mean remarks about others behind their backs.

Situation #6:

You see a student so drunk that he or she can barely walk stumble toward a nearby parked car, keys in hand.

Situation #7:

You are on a four-person team. There is a lot of tension in the team because the other two people think X is not doing his share of the work. No one has said anything to X about it.

Situation #8:

The two people who live (or work) in adjacent rooms across the hall from you have, on separate occasions, complained to you about each other.  One day, you hear them start to argue loudly in the hall.