People tend to use it to mean, "thing I don't like" far too often these days.

Slop has a long history as word used about art. Joeseph Cambell mentions it, people criticsed hollywood of it, publishers complained about it.

I remember those days using the term slop for lazy, uninspired, thowing anything that stuck on the wall, etc. AI is just a logical progression of the same term.

Slop has always had the meaning of low effort and non-artistic meant for mass production. It alludes to the vats of gray mush that would get fed to kids for lunch on an industrial scale. Or to the random mix of pig feed.