The moment before that slap, I thought Rickert would turn to the dark side, tempted by the past and what he wanted to relive the most, but NOPE! One page over and he slaps the shit out of that cretin, tells him off, and walks away.
Everyone here is right about his balls, and not for the sole reason of slapping Griffith, but for doing so on his den of lies! Surrounded by demons, madmen, queens, seers, people who warship him to no end, to do this while in the company so many incredibly powerful individuals who would tear you apart for looking at Griffith the wrong way, that's some real balls right there.