A term used by prog fans to describe other, non prog fans, such as AC / DC, Slayer, and others. In music, 4/4 is common time signature, while prog as different time signature changes through songs.
Person 1 : "I like thrash."
Person 2 : "I prefer prog."
Person 1 : "But we still respect each oth-"
Person 2 : "Get that 4/4 pleb shit out of my face, you pleb"