Ban "GG"
GG is a phrase that should automatically be blocked. I just had a team surrender 4-1 at 20 when we were only down by 13 kills and had taken more towers than the other team, and had literally just finished getting a double kill. Our Tryndamere said "gg" after his third failed gank at about 12 minutes.
When someone says "gg" in team chat, it kills morale instantly. It subconsciously gives everyone the impression the game is already lost while simultaneously letting you know that at least one of you has given up entirely. If people would focus on playing instead of spending their time whining about how the game is already lost, they might find the tide shifting.
Furthermore, while we're at it, there should be more visual feedback for how pushed a lane is. Kills are important for momentum, but at the end of the day, you don't win the game by killing the other team 50 times. You do it by taking their nexus. I've been in at least three games I can remember where my team has won with a final kill count of about 20-50 because we stayed mobile and pushed effectively. And I've been in several more where the other team did it.
So many people are caught up watching self-styled "athletes" get astounding kills on eachother at Worlds that they fail to realize there's more to winning a game of League than getting the penta. So please Riot, censor "GG", or at least let people know at a glance that their team has control of the map despite being down in kills.