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