What is the opposite of a pickpocket?
Without your awareness, a pickpocket will pull some object from your pocket or your bag.
What can we call somebody who does the opposite action, pushing something in your bag or your pocket?
Edit after comments
I asked this question to know if, in English literature or usual expressions, there were an expression which corresponded to this completely unusual behavior; it is the stage that corresponds in a scenario current from limning.
Putpockect put in a text where it is a matter of pickpocket, seems clear, and for no English-language
Reverse pick-pocketing is in fact the art of placing one's own objects into the possession of another, either for entertainment or a charitable matter. However, the correct, street credible term, is putpocketing
[Urban Dictionary]
So it's reverse pickpocketing. It's something you don't see every day.