Defeat the Meth Tweekers while wearing the Evil Cartman goatee and the bald cap.

*Missable*

The goatee is located in Cartman's bedroom. Loot it from a dresser. The bald cap is in the bag in Romper Stomper's cell in the police station. You must go to the second floor, shoot open the vent, go into the locker room, loot the jail cell key, then unlock his cell and loot the bag. Make sure to equip both. You need to wear them before you go to Kenny's house during the Calling Banners main story quest to recruit Tweak. This is one of the first quests in the game, so make sure you go to the Police Station right away. After you defeat the Meth Tweekers, the achievement will unlock.