Pick 50 pockets
If you have, like me, problems getting this trophy by the ways described in several guides and videos (for example using Sarah in Vault 21) because you always get caught, even with a Sneak skill of 100+ and a Stealth Boy, see what helped me:
Go to The Fort and climb the hill up to the big gate that leads into Ceasar's camp. On the outside, there stands a guard at the cliff with his back to the big gate, on the inside there is a guard standing on either the left or the right side of your way just after entering. You can always hide behind a wooden pole and pickpocket him from there. BUT FIRST you have to switch on the Hardcore mode so that you can steal his ammo one by one (it counts everytime you pickpocket something and leave his inventory) and you should use your Stealth Boy. It sure takes some time, but what I did was to simply pickpocket him like this, one gauge at a time (when the karma messages pops up it should count for the trophy but you can always check in your PipBoy) and save after each succesful pickpocketing manually (if you use Select for autosaving your Stealth Boy immediately wears off). When he doesn't have anything more in his inventory with no weight, switch to the guard in front of the gate and do the same, then switch back again. It worked for me and while using the manual save the pickpocketing worked almost every time.
I also undressed, switched the game difficulty to Very Easy and left all my inventory on the floor - don't know if that affects your success, but nothing else works you might as well try it that way.
I wish you luck - because apparently that's a big factor for this Trophy...