Here is the full list of all 23 POSTAL 4: No Regerts achievements.
Finish all rampages
Finish a mission with all 3 Dudes
Reunite with an old enemy, again
Collect all Krotchy, Kunny, & Larry collectibles
Collect all the paintings in the game
Beat the Fix Race errand by crossing the finished line with a fully bloodied scooter
Kill all of the mountain men on Thursday
Kill 4 fast-food workers during the Mexicleaner errand with the FOURnicator
Kill 100 pigeons from thrown cages
Get all 10 petition signatures using the drag outfit.
Find the secret crack den!
As the Cat Dude, kill 10 chicks
Hit all barrels with an immigrant during the Border Smuggler errand
Kill 7 people at the same time using Dude Eye
Beat all highscores of the Scooter Challenge
Turn 10 toilets yellow with piss
Reach maximum heat level with the police and survive!
Run over 50 people with the mobility scooter.
Flush after taking a piss in a toilet
Make your homeless sign
Install all bidets for Mike without killing anyone
Beat the game by only using kicks to open doors and kill people
Completed the story with no kills