Hubris, in this day and age, is another way of saying overly arrogant. You can tell the difference of hubris and just regular arrogance or pride by the fact that the character has seemed to allow reality slip away from them. The character portraying hubris, also commonly referred to as hybris, may have just gained a huge amount of power and the false belief that they are “untouchable”.
The term hubris used to have a slightly different meaning and was a very negative subject back in ancient Greek. It used to be closely related to a crime in Athens. In writing and literature hubris is generally considered a “tragic flaw” and it is saved for the protagonist. The reason for this is because at the end of the story you should be able to see that it is this flaw that brings the “bad guy” down.
A classic example of hubris is featured in Shakespeare’s play Macbeth. Macbeth, the protagonist, overfilled with ambition and arrogance, allows his hubris to think you would be able to kill the valiant Duncan without penalty so he can claim the throne of Scotland for himself. Obviously murder is highly frowned upon, so this eventually leads to Macbeth’s demise as well.