This can probably be done anywhere, but I got it in Chapter 3, near the end. I systematically took out all the enemies in the area and in the buildings, saving frequently (using the mirror portal in the back room on the lower level of the main house). I hadn't released Chainsaw Guy yet, but there was one final enemy near the far gate that you have to go through to finish the level. I just snuck through the house on the left side near that area, to the open window, hiding. When the last enemy turned and started walking away from the window, I climbed through, threw a bottle (there was one by a wall in that same building, near the first of the two wall switches), got close, crouched (with R2) and stabbed (with X) to get the trophy. I had to try a few times because the enemy doesn't stay stunned very long, and I tended to miss my throw, but with the save point being not far away and having taken out all the other enemies, I could pretty much hurry back to where I needed to be after re-loading, for a second attempt.