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