First of all — try talking to that person. Good communication quite often can solve a lot of problems. If that does not help and someone in the drawing spoils fun for everyone, you can prevent them from drawing altogether:
Make sure you're the admin of the drawing
Open the drawing Admin menu and change Own layers and Add/remove layer settings from "All" to "Approved". Warning: this will prevent everyone else from drawing as well. Make sure you follow the next steps as well.
Kick on the avatar of a person causing trouble from all the layers. They won't be able to rejoin a layer.
Change all other people's roles to “Approved”, so that they can continue to create and join layers.
