On the surface, the word seems similar to 'pickpocket,' but it has a whole different meaning. A pocket picker, similar to a 'prison princess,' is a person who hangs onto the pocket of stronger, more dominant prisoners, mostly referring to gay people. It can also be used to refer to someone who is so far up someone else's ass that you can see the hair in the back of their throat.
Male 1: Yo, you hear about Male 2? He started picking pockets. People are calling him a pocket picker.
A weak person in prison who is turned gay
Man 1: Did you hear about Jack? He became Harrys prison princess