On any page that displays a grid of Pens as live previews, or in the editor itself, you can disable the JavaScript with this query parameter at the end of the URL:

?turn_off_js=true

This can be useful if you find (or accidentally create) a Pen with JavaScript that is taking too long to run — for example, a Pen with a loop with so many iterations that it hangs the browser. With JavaScript turned off, you can go into the editor and update the Pen, or go to your profile page and delete it. JavaScript will still run on the parent page, so you can save your changes.

Examples of places you can use it:

In the Editor

http://codepen.io/bound20/pen/JiLno?turn_off_js=true

On Your Profile Page

http://codepen.io/chriscoyier/pens/public/?turn_off_js=true

Once you've corrected or deleted the problem Pen, you can remove the query parameter from the end of the URL and refresh the page to let JavaScript run again.