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