This achievement can be gained by exploiting the fact that pickpocketing the bubblegum or the beer from Sarah Weintraub (in Vault 21) does not actually remove it from her inventory. If you equip a Stealth Boy and have Lily Bowen as a companion you can repeatedly pickpocket Sarah and gain the achievement quickly. If you are fortunate and/or skillful you may be able to do this before a single Stealth Boy runs out.
This achievement can be attained by pickpocketing 50 items on a single or multiple characters. In order to count toward the achievement, items must be selected and removed individually, and the inventory has to be closed after each theft.
Pickpocketing items that have no value (such as bullet cases) will not count towards the challenge or achievement.
Reverse pickpocketing does not contribute to this achievement.
Even with the Stealth Suit from Old World Blues and 100 Sneak in addition to using a Stealth Boy, Sarah can still catch you pick-pocketing.