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