By owner:
You can choose to disable captioning as a owner of your media.
- Go to your video, click on Actions > Edit
- Click on Captions tab, and then for the caption file you do not want to display click on the icon "Don't Show On Player" (see below)
By viewer:
As a viewer, if you see captions and would like to disable captions on a video shared with you...
Click on the "cc" icon on the player, and select 'Off'.