Pardon!G 50

You'll unlock this achievement for messing with the police officer (fighting him) and you should be able to unlock it fairly easily. I was able to on my first attempt and with literally 0 health left. It will only take a few hits to take him down. Make use of your special attacks, I found the low kick most helpful, and definitely dodging. Cops deal a lot more damage than the other enemies and can take you down in as little as 2 hits. You'll see on the video I have posted below that I started the fight with 4 out of 5 hearts and after only 1 hit from the officer I was down to literally 0 left. If you're able to get behind the cop or able to piss in his walking path as he is walking towards you and making him slip that will give you some advantage (if you're skilled unlike me, you'll cause him to slip and won't fail like I did).
The first cop you will encounter is near the end of level 2 however, this is not where you will be unlocking this achievement. You'll just want to avoid this cop. The next one you encounter and the one where you will be earning this achievement is during level 4. Here's a video of when I unlocked it: