I'm wondering what plugin/theme is used for the comment flagging options (insightful, off topic, LOL etc) found on vanillaforums.org.
Are there plugins available or is this custom code only available on the vanilla site?
No to first part. Yes to second part.
search for the closed discussion on the reactions plugin and hopefully
closest is this http://vanillaforums.org/addon/likethis-plugin
I may not provide the completed solution you might desire, but I do try to provide honest suggestions to help you solve your issue.