Youtube – Clear “view history” on YouTube

YouTube Help has a solution on this.

To clear your viewing history, follow the steps below:

1. Sign into your account, and click the account link at the top right of the page.
2. Under "My Videos" click the History option.
3. Click the "Viewing History" tab in the gray bar to see videos you viewed since you opened your browser.
4. To clear it, click the "Clear Viewing History" button at the top of the video list.

Go directly to your Viewing History.

When searching for videos on the site, you can turn off search suggestions as you type your query into the search bar. Please follow these tips to turn off search suggestions as you type:

1. Type your search query into the search bar at the top of the page. Click the "search" button.
2. On the right hand side of the page, click on advanced options.
3. A window will appear. Deselect "Display query suggestions as I type". You have now opted to turn off the search query suggestions.
4. Finally, click the "search" or "close" button on the window to exit the "advanced options" window (and return to the page you were on before).