If you look carefully at the original episode of the fifth episode or the later episode of My Little Brother's Memories (about 20 minutes), you can see that the hostess only said FK with UC in the middle, so it is generally "hey, fuck you", which means "hey, fuck you"

PS: In the original clip, UC is said to be behind. You can see her mouth shape in 20 minutes. As for how Kai Zhe died, he was punished for rebelling, and he will know when he updates it.