You must buy the Dave Hasselhoff nose job from Tom's Rhinoplasty before going to Clyde's house at the end of the game (right after befriending the girls). This will cost you $175. Then you must beat the game (Kenny) while "wearing" this nose job. If you don't want to have to waste $175 on this so you can spend it on equipment, create a save after you befriend the girls, get the nose job, finish the game and get the achievement, then revert saves so you don't have to waste the $175 and can spend it on equipment you need.
This should be paired with "Two Girls, One Stick" and "Outpatient" achievements. All three can be gotten simultaneously.