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