On the December 20 installment of JTBC's 'Witch Hunt,' Sung Si Kyung recalled a moment he was chided by fellow singer Kim Jong Kook for not giving a proper greeting.

Sung Si Kyung said, "Before I debuted, I promised my manager that I would sincerely greet people I knew, but not those I didn't.  Thanks to that, I was greatly criticized by strangers."

He continued, "Originally, I was close to Hong Kyung Min but not to Kim Jong Kook so I greeted the former in a familiar way and the latter in a hesitant way. Seeing the starkly different greetings, Kim Jong Kook chided me saying, 'From now on, let's do it properly.'  Since then, I've been doing it the right way."

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However, it turned out that Sung Si Kyung was not the only one who had to go through this as the other cast members could sympathize.

Shin Dong Yup said, "I don't know about other people, but you just have to do it properly to Kim Jong Kook," while Yoo Se Yoon said, "One time, Kim Jong Kook told me he would hit me," making everyone laugh.

If you know Kim Jong Kook, you know how muscular he is so it would probably be wise to heed the threat!