Nick has violent tendencies, but he rationalizes these tendencies by only being violent toward people he thinks deserves it. These two tourists are innocent, so Nick is aghast that his friends attack them—and so he defends the tourists.

Nick is very protective of his mother. She is also very protective of him, so it's a relationship that works out well.

Here the fact that Nick's mom is a single mother is alluded to, and it helps explain why the two are so protective of one another. But why is Nick's dad out of the picture? Does Nick think he is better off without his dad in the picture anymore?