Lee Kwang Soo is known as a “betrayer” in Running Man due to his nature of wanting to win at any cost, even if it means playing a little “differently”.
Lee Sang Yeob might have pulled one of the greatest pranks on Lee Kwangsoo and gave him a taste of what betrayal/being tricked feels like. The members of the Running Man cast were playing a game where they had to keep track of the steps on their step counter. Once HAHA started looking for his, it was gone. The first person he went to was Lee Kwangsoo and he even slightly cursed at him due to him knowing Kwang Soo’s betraying nature.
Lee Kwang Soo felt that it was so unfair that he even started cursing at HAHA and tried to prove his innocence.
HAHA knew his gut reaction was correct when he found his step counter with Kwang Soo and knew that it was his doing, right?
It was revealed to be Lee Sang Yeob that was behind everything and put the blame on Kwang Soo because he would be an easy target. He was the one who was using the step counter.
He even slickly saw the right situation to put it into Kwang Soo’s pocket and acted as great as you can in this situation, he showed no signs of being the one who planned all of this.
All of this even got Kwang Soo to start questioning his mind and sanity.