This is a story related achievement and you'll get this during your third night out on the town, investigating the police station.
At the end of this quest will be a boss fight that is a bit different than ones you've fought so far. In order to win this fight, you need to drain the bosses health by knocking enemies back into the striped red squares. The boss has 9999 Health and will take 2500 per enemy caught in its attack that reaches said squares. The best allies you'll want for this fight are Super Craig and Captain Diabetes as they have the best knockback abilities among your allies. Mysterion has a reverse knockback ability as well but I found it a bit more difficult to get the enemies where I needed them.
The main thing you want to do is stay on the far left plane of the battle field as during the first part of the fight, the boss will have an attack that will take the first few columns closest to it and will unleash an attack doing 9999 damage, After this happens, the danger zone will be reduced and this is when you'll need to knock the enemies back into the danger area so that the boss will attack them and deal damage to itself.
This can be annoying as sometimes you'll be pushed to the far right on the battlefield and the enemies have a knockback attack as well. You're also on a timer with the bosses attacks, much like the "fight" against Bootay in the strip club and use your Glitch TimeFart to skip an enemies turn if you need it. Quickly run to any available squares in the safe area and let Super Craig and Captain Diabetes do all the attacking with their "X" attacks to knock the enemies back into the danger squares.
Once you get the rhythm and battle flow down, just have Craig and Scott do all the work and you'll come out victorious.