Sheldon Cooper is at the center of nearly every episode of The Big Bang Theory. As the show's breakout character and de-facto lead, he's the protagonist of most storylines. Most make full use of his character's quirky and obsessive personality to great success, highlighting how much he changes during the show's twelve seasons.

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However, some storylines feature Sheldon at his worst. He's morally reproachable, selfish, insensitive, and just plain rude. The show often finds excuses for his behavior and, most of the time, they work. But there are other times where there's no way of justifying his actions, and the audience questions why anyone would ever be his friend.