You know its GG when i pick Shaco

You know its GG when your mid picks up more then 2 dorans ring

GG when everyone gets Teleport and Revive

You know it's a GG when 1 whole team gets Promote and Revive, the other whole team is all tanks, and both teams send every single champion down mid lane without saying a word to each other beforehand.

True story. Two 5-man premade troll teams. :P

(My team beat the tank.)

You know its a GG when your jungler is AD Syndra who starts off not buying anything and claims is going to use the gold to buy IE when it adds up.

You know it's a GG when your Kat runs Clarity.

You know it's GG when you have shen, amumu, and malphite in a 3v3 and you all hit lvl 6

true story, we were down 0-10 and we still won cause of our ults

You know its gg when you have jungle talon that dies to blue WITH A LEASH and feeds enemy mid
(True story)

You know it's GG when your Nasus farms top the whole game,gets 200 CS, and still can't win the game when Nasus' team is ALREADY winning.
(true story, Nasus built retarded and rushed yomu's and frozenheart against a chogath.)

You know its GG when your jungler is a complete moron who feeds the enemy mid 15 kills, in the first 20 minutes!

Just happened a few games ago.