Question: > 
> **This guy's alright in my book**, because he used the word "rapscallion". 
> 
> 
> [Source](https://meta.stackoverflow.com/questions/378976/unexplained-clutter-in-a-post-edited-back-in-by-author/379059?noredirect=1#comment663338_379059)
> 
> 
> 

What it means by alright in my book?

Answer: 
"In my book" means "in my opinion", "according to my belief system". The commenter approves of the other person's vocabulary.
That means he likes the way that guy wrote because that same guy used a word he particularly enjoyed.