You get up, tell the teacher she's nice, or if she's not, just say it's an emergency, you have to go to the bathroom, and, um, you know, handle your business. Um, let's see... Wipe off as much as possible, get some, uh, some soap from the restroom, and if you can find a bottle of water, dip your underpants in the water. Drench it out, you know, until the dookie is mostly gone, and then you should be good.

Sit there and suffer.

Enough time has passed.