PALO ALTO  (AP) — The principal of a Northern California high school is putting an end to the tradition of students streaking across campus.

The ban came after a couple of boys took off everything and ran across the Palo Alto High School campus on the first day of school Thursday.

“Typically this type of behavior has occurred during the end of senior year prior to graduation,” Principal Kimberly Diorio wrote in a letter to parents. “In my six years at Paly, it never has happened on the first day of school.”

She said streaking at the start of the school year creates a negative environment at the school. Students who participate in naked tomfoolery could face suspension and a talk with school police, she stressed.

Streaking is a popular tradition at the school, but students tell the San Jose Mercury News some have become more brazen with the routes they run and the costumes they wear.

Senior Vivian Laurence said that when she was a freshmen, a group of nude guys carrying live chickens crashed her girls football game, throwing the clucking, flapping birds to the ground before racing off.

Sophomore year, another bunch of boys wearing only cowboy tops rode stick horses through campus. And the end of last year there were several streaking incidents, including one that had about 20 female students dressed in the barest of Native American accouterments who bolted across the grounds, letting out whoops and hollers.

“Last year was pretty excessive,” Laurence said.