Urban Dictionary describes a Squeaker as follows:
“A person over an online game with microphones who has an annoyingly high pitched voice, often under 11. Squeakers commonly get upset over every bad thing that happens to them, taking it out on fellow players through loud shouting and mass amounts of swearing and name calling. Commonly found in popular FPS (first person shooter) games ex. Halo 3, Call of Duty 4, Battlefield 2 etc.”
Example of a Squeaker in video above, now this is not really a 11 year old playing Grand Theft Auto 5. But a guy by the name of Lui Calibre who goes on-line and impersonate a squeaker and annoys anyone on-line who is playing with him. I encountered such a 11 year on Destiny the other evening, to say that he spoiled a Vault of Glass raid and the rest of my evening is a understatement. But on the flip side it is the only negative experience I have had playing Destiny since buying the game 4 months ago.