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