As a default setting, YouTube.com tracks both your Viewing History and Search History. Here are the YouTube.com privacy settings to disable the collection of this information.
1. Login to your YouTube.com Account.
2. Go to www.youtube.com/history
3. Select the Videos you want to Remove from your YouTube Watch History then click [Remove] or click [Clear all watch history]. Click [Pause watch history] to disable the collection of this information by YouTube.com and secure your Internet privacy.
4. Go to www.youtube.com/my_search_history
5. Select the Videos you want to Remove from your YouTube Search History, then click [Remove] or click [Clear all search history]. Click [Pause watch history] to disable the collection of this information by YouTube.com and secure your Internet privacy.
Reference
YouTube.com – Viewing History