Default Illegal Activities
You can be arrested for these actions
Assault/Murder: Killing/attacking a user outside of self defense is illegal, and can result in lethal action from police.
Raiding: Having the intent to invade another person's home. Whether you're being harmful or not, trespassing someone else's house should be considered a raid.
Mugging: Mugging somebody through the E menu on specific jobs.
Stealing: Unlawfully taking possession of someone else's property such as a boombox or other entities. 
Kidnapping: Knocking someone unconscious with or without the intent to kidnap them.
Disrupting the Peace: Causing a disturbance in public space or highly populated area. 
Making Drugs: Possession of drug making entities, plants, illegal seeds or meth lab are all grounds for arrest. 
Having Printers: Money-making entities such as printers or mini-printers are illegal. Bitminers are legal unless specified otherwise by the Mayor. 
Having a firearm without a license: If you are searched and possess a weapon without a license you can be arrested. Police may randomly search you if they have reason to believe you possess an unlicensed weapon, but it is a hostile action and you may fight back.
Weapon Modifying: Modify weapons for upgraded stats is illegal. 
Processing Weapons: Using or possessing a Processor is illegal. 
Hacking (As the hacker job): Hacker job is not illegal, but the action of hacking something is. 
Selling Illicit Goods: Advertising illegal entities such as drugs or seeds is illegal. 
Being an AOS job (Gru, Abomination, Mr. Sniffy and serial killer): If your job is listed as AOS (arrest on site) you can be locked up at any time for any reason.

Prank calling emergency services: Making prank calls or false reports to the CP may result in you being arrested.

Performing any illegal activity may result in consequences such as being arrested or fined. You may even be killed if you are presenting an active threat like assaulting or killing people. Resisting arrest may result in death if you present a threat to an officer. Allowed to fire back if fired upon( goes both ways)