Here is the full list of all 27 Acorn Cop achievements.
Passed the test
Beat the boss acorn
Collected at least one Trump Balloon
Collected at least one Balloon
Collected at least one Baseball
Collected at least one Bed
Collected at least one Bra
Collected at least one Bus
Collected at least one Chair
Collected at least one Traffic Cone
Collected at least one Cop Car
Collected at least one Egg
Collected at least one Garbage Bag
Collected at least one Graduation Cap
Collected at least one Handcuff
Collected at least one Key
Collected at least one Ladder
Collected at least one Molotov Cocktail
Collected at least one Pile of Cash
Collected at least one Ring
Collected at least one Shoe
Collected at least one Suitcase
Collected at least one Tire
Collected at least one Flying Saucer
Collected at least one Underwear
Collected at least one Wheelchair
Collected at least one Apple