The term "I'm so dice" is a term commonly used by gamers to mean "I'm so cool" or "I'm so raw. It was originally created in the early years of D & D to be something one would say after rolling a critical hit, or the highest number on the dice, as if one were saying, I'm the best!" As gaming evolved and video games became more popular, it became popular for gamers all over to say I'm so dice whenever anything cool or amazing happened in a game that allows one to show off their superiority in that game, such as getting an amazingly high kill streak in Call of Duty, or being able to raid all dungeons in WOW. I'm so dice is really just a cool, popular term. It's so dice!
Gamer 1 (after seeing his friend get a 75 kill streak in COD): Dude! You just got a 75 kill streak!
Gamer 2: I know. I'm So Dice.