1. Open up a direct message with Donut.
2. Navigate to the home tab, and hit the "Don't pair me with..." button.
3. Add the Slack handle of the person you do not wish to be paired with directly in the drop-down menu and hit enter.
4. Open the drop-down menu anytime to view a complete list or to remove people from the list.
5. You're all set! Your "Do not pair with" list is applicable to all Donut channel(s) you join where groups of 2 are made. Your "Do not pair with" list is always confidential.