One game I was playing Battlecast Prime 
against a 
top, and I decided dance while I waited to last hit a minion. Then, the enemy starting talking to me in all chat about how he loves it, and he wanted a peace treaty. So for about 30 minutes, me and the just farmed and danced, with the occasional visitor. Sadly, the treaty had to end because people started to attack us, but it was hilarious while it lasted.
I can't remember any of the champions that were being played except that the jungler on my team was 
, 
mid on enemy team, and I was 
We were even with the enemy team in kills, towers and dragons and the game was sort of at a stand still. So pops into all chat and tells to join him baron pit for a dance party (yi had been ganking and smashing him all game.) obliges but not without the rest of us sneaking through the bushes behind him for back up. Sure enough, the whole enemy team is with in baron pit. The rest of us pop out of the bushes and join them in baron pit and we waste the last two minutes before he spawns dancing and joking with them in chat.
There were quite a few moments like that through the last half of the game. We'd meet up at empty buff camps and just hold dance parties. That match went on foreveeeeeeeeeeeer.
This isn't a moment that I thinking is my absolute favorite, but it happened recently so its fresh in my head.
So im in a 4 Stack with 3 other friends, Im going AP Kog'Maw Mid, and my other friends were going Yi, Lux, and Urgot. We had some random who was going Nasus, but that's irrelevant to the story (and so is the Yi). About a minute prior to the enemy surrendering at 21 minutes since we were stomping, my friend on Urgot decided to royally screw me over.
Me, My Friend on Lux, and Urgot went to chase (and kill) the enemy team's Kalista and Udyr.
We failed to notice the enemy Gnar who tp'd nearby, and was coming at us quickly as Mega Gnar.
Urgot was standing right next to me.
and then he decided to ult Gnar...
This placed Gnar directly next to me, while he was mega and his ult still up.
Gnar did terrible things to me and shortly died thereafter.
I Yelled at him for that did not yell at him for that
and then we won about a minute later.
