You've probably done all the obvious stuff, so my guess is that you haven't done/won one of the mini game activities. Make sure you've won at least one game of darts, pool, bowling (has to be a full game, not half) or maybe get the high score on Qub3d. Plus make sure you've actually done the other things with friends like strip club, cabaret/comedy club, eating or drinking at least once each.
Have you also got all (remaining) friends to 100% like/respect...? I can't remember if that's required but if all else fails give it a go.