A book

Used as an analogy to something very difficult and say it as an easy thing to piss people off thinking you as an arrogant asshole.

You can use this analogy when you make something so hard to do easy as fuck. It helps inflate your ego too.

Cassidy: Damn! This calculus exam is very difficult. There's no way someone can finish this under an hour
Brian: *Answers 6 questions and skips all the other ones and passes his papers* Dude this is so easy to understand. It's like reading a book. I don't why are you guys having a hard time on it
Cassidy: Shut up asshole!
Brian: Cassidy, your dad is literally black.