Here is the full list of all 26 POSTAL: Brain Damaged achievements. It takes around 10-12 hours to unlock all of the achievements on Windows.
Kill the big bad RONA without using the vaccine
Kill the big bad RONA
Kill a certain group of hostiles in the forest
Confuse at least 5 hostiles with piss
Use the steroids powerup
Use a health pipe
Kill Karen
Use an ammo box
Use portable armor
Burn at least 5 hostiles with piss
Use the akimbo powerup
Kill a certain group of hostiles in the neighbourhood
Pet a cat
Freeze at least 5 hostiles with piss
Kill Tesloborgelion
Find the third installment
Use the quick pillz powerup
Find a certain secret not on wednesday
Get 100% on any of the levels
Piss on Tesloborgelion boy parts
Find all enemy codex entries
Find all location codex entries
Find all weapon codex entries
Finish any level below the speedrun threshold
Find a certain secret on wednesday, my dude
Reflect 10 projectiles