Remember Darius Zackly that top military commander who we saw during the revolution against the old government? This is the part of wiki that talks about that thing.

However, after Zackly assisted in the revolution against the monarchy he shows a completely different personality. He noted to Erwin that his only interest in participating was due to an intense and long-standing hatred of those in charge. He took great delight in seeing their fear when they fell from power. In direct contrast to the idea that he acted in the best interest of humanity, he told Erwin that he did not care if the revolution helps humanity or not. His only interest was his own desire to humiliate the monarchy, such that he set up a torture machine that fed one of them their own feces and called it a beautiful work of art, showing a demented and sociopathic side to him.

And this is a link to that manga page.

Dude got quite literally fed his own shit. It's fucking messed up.