Comment by jknoepfler

That's a very dodgy etymology. The use of "slop" to refer to trashy content dates back to the late 19th/early 20th century, long before the advent of the internet.

I think our tendency to attribute "novel" word usage to 4chan might reflect more on us than on our language.

I'm a little short on primary reference material, but here's an example from 1917: https://www.gutenberg.org/cache/epub/22692/pg22692-images.ht.... Conversation on language log has at least two others from 1897 and 1920 respectively.