A superficially clever way to agree with a statement made on an internet forum. Reads and sounds somewhat silly since the correct word for pointing to someone else's post would be "that". "This" would be the word you would use to point to your own post.
Forum poster #1: "The schedule TV model is dying. If you don't give me on on demand viewing option then piracy will always be something I will consider"
Forum poster #2: "This." ...
Forum poster #3: "This what?" "Oh you meant THAT. Ha ha, I get it, very funny"