I dunno, stealing that Titan alone from the airport and flying under a bridge just cuz, even though I'd have to restart the mission? I felt pretty BA so it was worth it (and I made it back in one piece).
I think rockstar said it would be distributed over time. I'm guessing alphabetically or by order you signed on into gta online. That or totally randomly. It is simply given to you with a little notification from rockstar.