You need the lavatory pass.
3 seconds sound clip from the Mean Girls (2004) movie soundboard.
You can hear this line at 00:04:25 in the Blu-ray version of the movie.
Quote context
[...]
- The first day of school was a blur, a stressful, surreal blur.
- I got in trouble for the most random things.
- I have to go to the bathroom.
- Okay. Can I have the lavatory pass?
- I had never lived in a world where adults didn't trust me, where they were always yelling at me.
[...]