What I love about them is that they have this dynamic that is kind of like everyone else's with Gwangsu (as in, bully bully bully) but it's different somehow, because by being the same age, Joongki is able to get away with being seriously mean. As in, dragging Gwangsu places and calling him idiot and making him do things that he doesn't want to do.
And then Gwangsu is like, totally sneaky, like, with everyone else he just lets it go or frames them or whatever, but with Joongki he'll get him back in secretly mean ways that I'll come to in a moment. But it's just super cute. Because to begin with, you're like, this is totally one-sided and unfair, and then you realise, wait, no. Because Gwangsu hits Joongki on the head with eggs.
I wanted to do this like civilized_era's post and put down as many moments as I could find/remember but she clearly has an elephant's memory because I can't remember where they went in half the episodes, never mind specific moments between Joongki and Gwangsu. So here are what I remember, and if you know any more, I will add them in :D:
EPISODE 7: Gwangsu arrives late, Joongki reacts reluctantly.
EPISODE 12: Gwangsu steals his answer from Joongki to stop him from winning the 7:1 challenge. Another secretly mean moment.
EPISODE 14: They both end up in the final of the "bibo" game during the thief round. Gwangsu reveals that he got "100 notes" from Joongki's fans, who is like "LOL REALLY?" and kind of embarrassed. Gwangsu keeps making Joongki and Gary jump up and down in their game and Joongki eventually just goes for the throat, so Gwangsu starts picking on him. once the game is finished, Gwangsu tries to make things better, essentially so that he won't get any more notes, but Joongki is like, NO >:|
EPISODE 15: Joongki keeps randomly jumping onto Gwangsu's back, most noticeable when they first walk onto the set.
EPISODE 16: Joongki is Gwangsu's wingman when it comes to Yuri
EPISODE 18: They share a room on the cruise ship and are the only two who are any good at waking up.
EPISODE 19: They act out a strange version of Joongki's drama. Joongki finds the whole thing hilarious.
EPISODE 21: when Gwangsu finally arrives at the right platform, Jihyo runs off first but Joongki stays and waits for Gwangsu to reach him before running together. then after Jihyo gets all mad at Gwangsu, Joongki lightens the mood by suggesting to buy fishcakes, and pats Gwangsu on the back. then Gwangsu apologises specifically to Joongki. Later on in the 1:9, Joongki helps Gwangsu to get Jaedong to say the line. and then when everything goes chaotic, Joongki keeps clinging on to Gwangsu and laughing
EPISODE 22: Gwangsu lifts Joongki onto his shoulders to help him get at the discounted toy. he sticks his head through Joongki's legs like he's done this before.
EPISODE 23: After being beaten up by Jihyo, Gwangsu decides that he's had enough and pretty much tackles Joongki to the floor.
EPISODE 25: They are both characters from Candy Candy in the opening segment and fight for the same girl. During one of the team challenges, Gwangsu's hat is blown behind a display and Joongki gets on his shoulders in an attempt to retrieve it for him.
EPISODE 27: during the dance, Joongki puts his legs between Gwangsu's thighs without even looking. definitely done this before.
EPISODE 28: They are eliminated and sent to the prison together. They're given boiled eggs and play some weird rock paper scissors game in which the loser breaks the egg shell on the other's head. Joongki wins first and breaks his egg, but Gwangsu wins second but (purposely? I don't know if he's being secretly mean here or it's an honest mistake) doesn't break the shell when he hits it off Joongki's head. Joongki calls him an idiot.
EPISODE 29: On first hearing about that day's game involves choosing your own team, Joongki's immediate reaction is to call Gwangsu to find out what he plans on doing. Later, he eavesdrops into Jaesuk's conversation to find out where Gwangsu is and tries to convince Jongkook to go after him. During the balance game, while being in tight wetsuit and pressed up against each other, Joongki says that they need to trust each other. Gwangsu asks, "Do you trust me?" and Joongki is like, ...........sure.
EPISODE 30: Lots of talk about how Gwangsu is copying Joongki's fashion style. While searching for the guest, Gwangsu gets distracted flirting with some girls; Joongki appears and gets angry with him and tries to drag him (only him, Sukjin is there too but Joongki pays him no attention). When the girls' attention moves to Joongki, Gwangsu pushes Joongki off the stage with him. During the face pulling game, Gwangsu is secretly mean. When Jongkook annoys Gwangsu and Gwangsu randomly begins pulling his shirt off, Joongki grabs him and back-hugs him. To be honest, this entire episode should have just been titled, "Gwangsu and Joongki, bow chicka wow wow."
EPISODE 31: Gwangsu takes a huge bite of the bread stick while they're eating and Joongki purposely takes a tiny bite to make Gwangsu look bad in front of the hyungs.
EPISODE 32: Joongki is given chocolates which he then feeds to Gwangsu by hand. When they're both eliminated, Joongki runs and launches himself at Gwangsu's body in a move that is far too smooth to be the first time. they then go up against each other during the race at the end of the episode and Joongki jumps onto Gwangsu's back in order to be carried to the starting line. Joongki attempts to freak Gwangsu out but Gwangsu is just like "yah, am I carrying you? I can't feel anything." "Gwangsu and Joongki, bow chicka wow wow" episode 2.
EPISODE 33: Joongki is the one that Gwangsu gravitates towards when he first arrives.
EPISODE 37: Gwangsu again gravitates towards Joongki when he first arrives.
EPISODE 39: paranoid after the previous week, Joongki wants to make sure that they aren't going to get sprayed with water again. he convinces Gwangsu to turn around in order to spit water onto his name tag. after some protest, Gwangsu eventually trusts Joongki enough to let him do it, even though it could mean his early elimination. he makes sure to sit between Gwangsu and any member of SNSD. when Sunny tries to wipe Gwangsu's sweat away, Joongki yanks her hand back; he claims it's because Gwangsu isn't sweating, he's just splashed water on himself, but it looks pretty possessive.
Basically I think that this pairing could so easily just slip into this tragic, Lee Gwangsu angsting over Song Joongki the pretty boy with his legions of female fans and popularity and did he mention good looks, when in reality it seems more along the lines of, Song Joongki the pretty boy with his legions of fans angsting over Lee Gwangsu and covering that by being as mean as he can possibly get away with being on Korean television.
Put it this way, their theme song would probably be this.