Easy Achievement to unlock solo, just go into a solo / friends / crew only game and keep jacking cars until you get a text and onscreen message from an anonymous NPC saying something along the lines of "you're a dead man" or "You're going to end up on a slab", If you are in a solo game you have nothing to worry about. If in a friends or crew game just ask your friends / crew mates to not kill you or if you don't want to keep jacking cars just ask one of them above lvl 10 to put a bounty on your head.
** I didn't go into Los Santos Customs during my time on the run as I was doing missions for Soloman, and the achievement took just over 30 in game hours to unlock
(Text message and Bounty prompt on screen at 02:06am, achievement unlocked following day at 08:27am)..
** This was after the 2nd Title update on the 5th Oct.