If you click on the Save as my template link at http://jsbin.com/, it will save the current page as my template and display it when I come back to the page later.
How do I undo that so that I get a clean slate?
It may sound stupid but removing the content in both windows left and right and saving it as an template creates a blank state.
If you want to have the original template back here's the data:
Clearing your cookies for this site will also bring back this original template.