LONG BEACH, N.Y. -- Captain Underpants may be a superhero, but he isn't welcome at one suburban New York school.

Three 17-year-old girls were told to leave Long Beach High School when they showed up on the school's Superhero Day dressed as the subject of the bestselling children's books.

Captain Underpants is a superhero from popular books that has battled, among other things, talking toilets and the infamous Professor Poopypants.

The girls, Chelsea Horowitz, Ashley Imhof and Eliana Levin, wore beige leotards and nude stockings under white briefs and red capes. They were completely covered.

Principal Nicholas Restivo said he knows they weren't naked, but it appeared that way, so he sent them home. He didn't like the way they looked.

Other students were allowed to stay at school. They were dressed as Superman, Wonderwoman and other well-known superheroes.

One of the girls said she doesn't understand the fuss. Honor student Horowitz said of the costume, "They're not see-through or anything."

The principal said the girls could have worn gym shorts or even called someone to bring clothes to school for them. But the teens said that they felt forced to leave school. They all went home.

Horowitz said she and her friends did not want to wear "someone else's hand-me-downs" and that they had nobody else who was available to drop off clothes to school, Newsday reported.

Superhero Day was part of Long Beach High School's Senior Week. There were other thematic days during the week.