Blog Comment
Author, A. (year, month day). Re: Title of post [Blog comment]. Retrieved from http://xxxxx
Notes
Because the author is only identifiable by a screen name, that name is used as the author in the reference.
More Examples
Author, A. (year, month day). Re: Title of post [Blog comment]. Retrieved from http://xxxxx
AMO. (2014, June 14). RE: Seven lessons learned while being The Man [Blog comment]. Retrieved from http://librarianinblack.net/librarianinblack/lessons/#comment-82605