If you haven’t seen the episode yet, don’t read any further.
If you hold that Sandor was someone Joffrey looked up to then this would’ve been devastating to him.
^This. Honestly, I think the way Jack Gleeson played it was perfect. Watch his face crumble after Sandor says “Fuck the King”. I think the actors totally understand and acknowledge the dynamic of the Hound as a surrogate father figure to Joffrey, so to watch them play the scene like this was wonderful.