Not sure how nowadays Ukrainian perceive the word "Кацап" but for me it was always a term used for "plebs" in Soviet era psychedelic movie "Кін-Дза-Дза" (https://uk.wikipedia.org/wiki/%D0%9A%D1%96%D0%BD-%D0%B4%D0%B7%D0%B0-%D0%B4%D0%B7%D0%B0!)

Until today, I didn't even know that was a real word and I thought people were using a reference from the movie as an alternative derogatory term instead of "Orcs".

According to wikipedia (https://uk.wikipedia.org/wiki/%D0%9A%D0%B0%D1%86%D0%B0%D0%BF) the word is ancient and is targeting "Russians".

I am amazed how Soviet censure allowed usage of such a term in a movie which was as popular in USSR as "Star wars" in the west...

OP, thank you for your question. I learned something new today.