So?

1. What someone says In an argument to tell you to shut up or explain.
2. What a teacher or professor tells you so that you can explain your answer.

1.
Person 1: I'm telling you, we shouldn't be doing this!
Person 2: So? Nobody will find out. Anyways...
2.
Student: 2.
Teacher: So? Why is that the answer?

Nothing bad will happen

Something said by an idiot before something bad happens.

Person 1: Why did we go off the forest path, what if we get attacked?
Person 2: Don't be scared. Nothing bad will happen, okay?
Person 1: Is that a bear coming over here?!