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