A person who replies in a forum, when their point had already been refuted in the first, or previous posts. This happens because the person did not read, and responded blindly making themselves look like an idiot.
Hence the "TL:DR" in the name.
Person 1: *long, thought out, intelligent forum post*
Person 2: That is a bad idea, because of ____
Person 1: I already explained why that doesn't matter. Ugh, i bet you didn't even make it past the first paragraph you TL:DRetard