In order to obtain this trophy, you have to place a bomb into an empty enemy pocket.
I found this approach really effective:
1. buy the sleep bombs for Bentley
2. steal all the coins from an enemy
3. place the bomb onto the enemy and let it explode
4. make sure that you stand in front of the enemies pocket
5. quickly place 5 bombs into the pocket, walk away and let them explode
6. repeat this another 11 times until the trophy pops