A response to something of obviously little importance when it is exclaimed otherwise.

when you're hungover as shit after a spending a night drunk as a skunk

An arrogant person who thinks or acts like they are way more important than they really are.

A person who is a big shit

This maybe either because they are your best friend and you like to annoy them
Or because they are just an annoying asshole.
It is most likely that the person calls you little shit

When you get accused of murder and you have the big shit moment. Or when you take a big shit in the bathroom.

To trash talk someone a bunch of times.

The same as shit but with 1000 more pounds of crack with cocaine mixed all together so you can have extreme anal and porn.