Au contraire

From an AP wire story about a high school student running through his school, wearing naught but a gorilla mask:

The student told state police he had been dared by friends to streak through the school on Monday and had done so as a prank, said Sgt. Nancy Mazur.

and

"There's no way anyone in the district would consider this a prank," District Superintendent Linda Rice said Wednesday.

prank
noun
A mischievous trick or practical joke.

On the contrary, Ms. Rice, prank is the perfect word for it.