Here is the full list of all 50 South Park: The Stick of Truth achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
You defeated Princess Kenny while living with Dire AIDS.
You defeated Princess Kenny while looking like David Hasselhoff.
You defeated Princess Kenny in your girl makeover disguise.
While inside Mr. Slave, you summoned Mr. Slave.
You farted on the corpse of an aborted Nazi Zombie fetus.
You sold 300 junk items.
You've farted on every buddy in the game.
You accepted your fate and chose the name Douchebag yourself.
You befriended both crab people and gnomes.
In three separate battles, you've taken a shit in your pants.
You've spent $500.
You shat your pants during a boss battle.
You defeated Princess Kenny and recovered the Stick of Truth.
You defeated 20 enemies using Cartman's Ass.
You flung a turd of your own creation at an enemy.
You've farted on animals 25 times.
You made friends with half of South Park.
You befriended your father.
You have collected half of the available costume sets.
You opened all of the garages in South Park.
You defeated the High Jew Elf Kyle in battle.
You befriended the Goths, like everyone else playing this game.
You've let Kenny die in combat 10 times over the course of the game.
You collected 15 Chinpokomon.
You successfully blocked every enemy attack in a single (non-tutorial) battle.
You completed your first day in South Park.
Over the course of the game, you've scored 100 perfect attacks.
Over the course of the game, you've blocked 100 attacks.
You have joined the KKK.
You've farted on people 100 times.
You've unlocked all of the upgrades for a New Kid ability.
You farted on 10 enemies in the world that were knocked out.
You defeated 3 enemies in one battle while your buddy was knocked out.
You collected 5 Chinpokomon.
You defeated the Grand Wizard Cartman in battle.
Gingers have bitten you 3 times without you blocking.
You defeated the Boss Hall Monitor while wearing freckles.
You found Jesus while playing as a Jew.
You completed the game without selling any items.
You farted on four major authority figures.
You've farted on a dog while in gnome form.
You knocked out 3 or more enemies with a single fart outside of battle.
You interrupted 5 channel attacks by using a fart.
You defeated the Meth Tweekers while wearing the Evil Cartman goatee and bald cap.
You watched your parents have sex for 60 seconds.
You completed the game and never ended a battle with your buddy knocked out.
You collected all of the Chinpokomon.
Everyone in South Park is your friend.
You've collected all of the available costumes.
You own all the weapons and costumes available in the game.