A kid between the age of 10-14 playing online FPS games while creating havoc using it's skill to annoy the rest of the people playing by using the online voice chat or by texting messages.
A great fear for other gamers is when a Shit Kid develops interests for other games, but fear not. If you encounter a Shit Kid online simply Mute or Block the player and you should be fine.
PS. Please note that thanks to the sharp and squeaky voice of a Shit Kid, may cause serious damage to your ears and if not treated right will cause your sense of hearing to decrease.