No, you don't get it for killing a rockstar developer. You need to have been in at least one TDM/DM with rank 1 or above. That is what I believe anyway, as I was on Rank 2 after playing the missions (such as Bomb Da Base II etc) with Macey.(I didn't play any other game apart from freeroam and race). Then a few days ago, me and Mace played a deathmatch party game with other contacts on our friend list. I then got the chance to be a zombie.
grimmy is a gay icon