In the first episode of JDJ, the main character brings a vase of dung and proceeds to throw it at Yi Inim's servants as well as the gifts given to to him. He would repeat this in a later episode, this time that it is from the people. While this scene was probably made up for the show, it turns out something like this did happen in Korean history. Not in the medieval ages, but the modern age, specifically the 60s.
The historical figure, Kim Duhan, has been brought up a few times here, but not alot. Kim Duhan is a Korean gangster who fought turf wars against the yakuza during the colonial period, eventually becoming an assemblyman sometime after the liberation. He has more or less become a Korean folklore hero for his fights against the yakuza and has been dramatized in movies, like The General's Son, played by then newcomer Park Sangmin (GKS Crown Prince Yangnyeonggun), and SBS' Rustic Period (Yainshidae), his younger self played by Ahn Jaemo, his older self played by GKS actor of Taejong. Kim Duhan is also the grandfather of actor Song Ilgook.
Basically, in 1966, Kim Duhan started speaking out in the National Assembly. I wasn't able to understand entirely what he was saying, but basically he accuses the politicians there of being thieves, and proceed to throw dung water at them. This incident made headlines, and according to my father, its a pretty infamous incident, even to this day. There are even photos of what happened.
The incident was dramatized in the SBS drama, clip provided here.
There is no way the scene in JDJ was not inspired by this incident.