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 farted on four major authority figures.
You befriended both crab people and gnomes.
You defeated Princess Kenny and recovered the Stick of Truth.
You defeated Princess Kenny while living with Dire AIDS.
You defeated 20 enemies using Cartman's Ass.
You opened all of the garages in South Park.
You farted on the corpse of an aborted Nazi Zombie fetus.
You've farted on every buddy in the game.
You befriended your father.
You watched your parents have sex for 60 seconds.
You interrupted 5 channel attacks by using a fart.
You defeated the High Jew Elf Kyle in battle.
Gingers have bitten you 3 times without you blocking.
You made friends with half of South Park.
You have collected half of the available costume sets.
You've spent $500.
You've let Kenny die in combat 10 times over the course of the game.
You collected 15 Chinpokomon.
You defeated the Grand Wizard Cartman in battle.
Over the course of the game, you've scored 100 perfect attacks.
You befriended the Goths, like everyone else playing this game.
You flung a turd of your own creation at an enemy.
You completed your first day in South Park.
In three separate battles, you've taken a shit in your pants.
You have joined the KKK.
You knocked out 3 or more enemies with a single fart outside of battle.
Over the course of the game, you've blocked 100 attacks.
You've farted on animals 25 times.
You've unlocked all of the upgrades for a New Kid ability.
You defeated the Boss Hall Monitor while wearing freckles.
You shat your pants during a boss battle.
You sold 300 junk items.
You defeated the Meth Tweekers while wearing the Evil Cartman goatee and bald cap.
You farted on 10 enemies in the world that were knocked out.
You've farted on people 100 times.
You collected 5 Chinpokomon.
You found Jesus while playing as a Jew.
You defeated 3 enemies in one battle while your buddy was knocked out.
You successfully blocked every enemy attack in a single (non-tutorial) battle.
You accepted your fate and chose the name Douchebag yourself.
While inside Mr. Slave, you summoned Mr. Slave.
You completed the game without selling any items.
You defeated Princess Kenny while looking like David Hasselhoff.
You've farted on a dog while in gnome form.
You defeated Princess Kenny in your girl makeover disguise.
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.