Let's share our [best lagg moments]!
Mine just happened now.

Lagg during building mastery. playing atm with 0/5/5 [this is the mastery-ratio not my stats :P]. on ranked. My team will hate me ;O;.
Edit: I won with incomplete masteries :P irelia OT.

lagg during champion select, granted me with kayle and my mate with brand, randomly, we won thou.

Giant lagspike as Twitch during a teamfight.

Of course I assumed I would die, it lasted like 10 seconds or so...

When it ended I was at 50% hp with 4 extra kills.

Awesome lag on the opponents team just now.
Morde and Jarven initiated, then stood around and did nothing.
Lategame
at the Baron.

I can only imagine the enemy teams faces, we were dominating but not ahead a lot, well, this one settled it, thanks riot

You gotta hate when you take the wrong runes on a rune dependant jungler, happened me 2 or 3 times...

Just got the champion select screen hung up on my game, had to restart game and i'm standing on queue to enter . I <3 Riot.

Got lagged and randomly got gragas, I was gonna jungle so I had smite and flash.

We won.

I carried with a 7/2/14 gragas. It was ranked.

Lagg in a teamfight with Tristana.

Instead of sending the enemy champ right into my turret I actually pushed him the other way and helped him escape ~~