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