The adventures of Captain Undetpants by Dav Pilkey

One of the key and most important parts of the book and entire series is when George and Harold use the 3D Hypno ring on Mr. Krupp.

George and Harold use a 3D Hypno ring on their school principal Mr. Krupp because Goerge and Harold pulled a prank on the school football team (American football) by puting helium in the ball and replaced their heating mucle rub with extra strong itching cream and Mr. Krupp caught it on tape and blackmails them into doing jobs him like clean his car and mow his lawn every day.

So George finds an artical for a 3D Hypno ring and buys it. 4-6 weeks later they get the ring and take it to school to use on Mr. Krupp by making him look at it and when he is hypnotized the turn him into a chicken, a monkey and then turn him into Captain Underpants.

Then he runs off to fight crime and gets into some trouble with Dr. Dipper.

Now when ever Mr.Krupp hears someone snap their fingers he turns into Captain Underpants but when Captain Underpants gets wet he turns back into Mr.Krupp.