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.
Use a health pipe
Use portable armor
Freeze at least 5 hostiles with piss
Burn at least 5 hostiles with piss
Pet a cat
Kill the big bad RONA without using the vaccine
Kill the big bad RONA
Kill Karen
Kill Tesloborgelion
Find the third installment
Use the akimbo powerup
Use the quick pillz powerup
Use the steroids powerup
Find a certain secret not on wednesday
Get 100% on any of the levels
Confuse at least 5 hostiles with piss
Piss on Tesloborgelion boy parts
Find all enemy codex entries
Find all location codex entries
Find all weapon codex entries
Kill a certain group of hostiles in the forest
Kill a certain group of hostiles in the neighbourhood
Finish any level below the speedrun threshold
Use an ammo box
Find a certain secret on wednesday, my dude
Reflect 10 projectiles