Here is the full list of all 24 Naughty College 18+ achievements.
Give the poster to Linda
Fix the Printer
Take a picture of the exam answers
Hack into a computer with answers
Give the psychology book to Emily
Give the book to Marco
Meet Marco
Find the book for Marco
Hanna's trap
Water the flower for the first time
Meet Emily
Meet Linda
Meet Hannah
Meet Pitt
Start the game
End the game
Give the math book to Emily
Water the flower for the last time
Solve all of Linda's puzzles
Solve all of Hannah's puzzles
Lose all of Linda's puzzles
Lose all of Emily's puzzles
Lose all of Hannah's puzzles
Solve all of Emily's puzzles