Hello there,
I've been trying to find out how to complete these 4 hidden achievements in this game, until I finally discovered the description what you have to do in order to get the achievements.

1. "Bad Cop" Achievement
   Goal: You have to detain 100 people without reason.
   
   
2. "Musician" Achievement
   Goal: You have to hoot 100 times in a shift.
   
   
3. "Disaster on 4 wheels" Achievement
   Goal: You have to make 50 crashes which lead to cancelation of a mission.
   
   
4. "Fight Club" Achievement*
   Goal: You have to find a hidden teddy bear. (Teddy bear location is provided in the screenshots below).

• Teddy Bear Map Location[prnt.sc]
  
• Teddy Bear Interaction[prnt.sc]

Thanks for reading, hopefully I've helped you with your struggle if so, please, add to favorites and like! Thanks again! :)

EDIT: Thanks to Piierre for providing "Figh Club" Achievement explanation with screenshots!