"Ylaaargh!" is a general noise used to represent the sound of black people, especially those from West Indian origins, but of course, also any other black person. Although, not every black person is Ylaaargh - only a certain type.
It originated from the Edgbaston area of Birmingham in mid-2008 and has been around ever since. It first started as a variation of a black person saying "Yah" and alternative spellings include "thyaaargh" and "lyaaargh". It has to be noted that it only has the full effect when shouted.
Person 1: Look at there Ylaaargh over there
Person 1: Ylaaargh!