The act of having a whole conversation using comments. When two or more people feel it's necessary to use the comment section of a photo or video on Youtube, Facebook or otherwise social network instead of just calling one another or using a chat platform.
-That's a nice picture.
-Thank you! How are things Jason?
-Very well. I recently saw you on grandma's album of photographs kissingthe dog.
-Oh yes I remember! How is she?
and so the commentsation continues.
comment-say-shun, Noun, To have a conversation via Facebook, Myspace, Twitter, etc in the comment area. Usually results in useless notifications to people not taking part in the commentsation.