Yes, it was The Adventures of Huckleberry Finn but it's not what you think.

"A fifth grade teacher who is internationally-known for his methods and best-selling books was suspended for reading Mark Twain, says his lawyer.

Rafe Esquith, who teaches fifth grade in Koreatown's Hobart Boulevard Elementary School, was suspended by LAUSD back in March and has yet to return to the classroom. Although the district has not said why they are investigating Esquith, his lawyer told KCAL 9 that another teacher filed a complaint after he read a passage from Mark Twain. He says that if Esquith is not brought back to work by the district, he will sue.

[snip]

According to the L.A. Times, Esquith read a segment from The Adventures of Huckleberry Finn to his class, which includes the following quote:

The duke and the king worked hard all day, setting up a stage and curtain and row of candles for footlights.

At last, when he'd built up everyone's expectations high enough, he rolled up the curtain. The next minute the king came prancing out on all fours, naked. He was painted in rings and stripes all over in all sorts of colors and looked as splendid as a rainbow

[another snip]

Esquith, called "the world's most famous teacher" by the Washington Post, has written three best-selling books about teaching and is a critic of the overemphasis on standardized testing. His nonprofit, the Hobart Shakespeareans, raises money for school materials and had to cancel all of their performances this year."

http://laist.com/2015/06/18/teacher_suspended_huck_finn.php (emphasis about the snitch added)

So are you asking what the hell is wrong with that passage from the book and why was he suspended? The article does not say but according to Mark Steyn, where I found this story, 'Presumably it's a "micro-aggression" and the pupils might be "triggered"', whatever that might mean.

First removing Alexander Hamilton off the currency, now going after Mark Twain.