Toggle YouTube Comments
This Chrome extension is a modified version of JamieH's one, which toggles comment visibility with a button under the video, next to the flag. Unlike that one, this version toggles nothing other than comments, so page layout doesn't jump about when you click the button.
Installing
Click 'Downloads' at the top-right of the GitHub page and choose 'toggle-youtube-comments.crx'.
Alternately, clone this repo and point Chrome's extensions page to its directory in developer mode.