The opinion is literally a post on his social network account. The post is quite long, so it's able for him to evoke his opinion in detail. It also has good long discussion below. At first, I think just see it as a lecture note, but there is a problem: it doesn't have a title.
What should I do? And should I even do this?
I've read these questions, but all of them have the titles:
Believe it or not, there are guidelines on citing tweets (Chicago & MLA quoted there, others may be available) and you may be able to take a similar approach. (I like the MLA approach, which is reminiscent of the very old-fashioned approach of naming an untitled document after the "incipit", its first words...)
Alternatively, you could give it a placeholder title - Smith, J. (2015-01-01). [Notes on something]. Social network site. URL - here the URL is the key element to find it and the bracketed element is just for the reader's convenience.
As to "should"... if you would be happy to use this as a useful source had he published it in something unreviewed but with a title (eg a personal blog post), then the absence of a title shouldn't really be the problem...
