ok so im brining this news from x360a.org to this site..as u may of heard the rock dev achievement for GTA 4 was known as impossible..well i just finished a ranked match and killed a person with yellow underwear that had a rockstar logo on it and the person looked like a native zombie like character....then bam achievement unlocked....All u need to do is look for a ranked match and u get the achievement for killing the described above..achievement should pop up as soon as u kill the person..achievement is ''Let Sleeping Rockstar Lie"
im really sorry if this has already been discussed..if not then i hope this made ur day..