On August 2, KBS' talk show 'Problem Child in House' aired an episode featuring Sung Si-kyung as their guest of the day.
In this episode, the host Lee Chan Won mentioned Sung Si-kyung's friendship with another host Kim Jong-kook.
"You guys are close friends, right? Back in the day though, I heard that Sung Si-kyung, you got told off by Kim Jong-kook once."

He continued, "This one time, I went to see Hong Kyung-min, and Kim Jong-kook was sitting next to him. I'm not too sure what happened, but I don't think I said hi to him 'properly', whereas I did to Hong Kyung-min. With a straight face, Kim Jong-kook was like, 'Hey, say hi 'properly', okay?' I got so scared that I almost peed my pants then."
"You know how when you become an adult, you stop and think one more time before hitting someone, because you're worried about having a police record? He didn't actually hit me, but it certainly felt like he was beyond that point. He looked at me as if he was about to punch me hard. I was like, 'Okay, I must behave well in front of this sunbae at all times.'", he laughingly added.

He went on, "I mean, I was young, too. I'm not that of a square anymore!", then chuckled.
But Sung Si-kyung claimed that Kim Jong-kook has changed after working with entertainer Yu Jae Seok for years, "Kim Jong-kook has a different pair of eyes now. The look in his eyes changed over time. I feel like it's because he's absorbed Yu Jae Seok in him. One-third of his muscles are made of Yu Jae Seok, I swear!"
His remark at the end made everybody in the room laugh out loud, including Kim Jong-kook.

(SBS Star)