No missable achievements (plus 27 unknown)
Sign in with Steam or Xbox to track your progress, and:
Find a secret area.
Tip an exotic dancer.
Kill every enemy on a level.
Step in a pile of excrement.
Find the Doomguy in the Level "Death Row"
Complete "L.A. Meltdown" on any difficulty.
Kill 5 bad guys with one shot.
Use the hookah in High Times.
Use the Incinerator
Kill 1000 enemies.
Carry all weapons with ammo at once.
Finish a secret level.
Kill a Firefly Trooper while it's flying small.
Use a cheat code.
Find 70 secret areas.
Complete "Lunar Apocalypse" on any difficulty.
Complete "Alien World Order" on any difficulty.
Complete "Shrapnel City" on any difficulty.
Listen to Developer Commentary (Use at least one trigger).
Step on 40 enemies after using the Shrinker on them.
Find Sam in "Mirage Barrage".
Complete "The Birth" on any difficulty.
Finish the "Hollywood Holocaust" level in under 3 minutes.
Finish any level on "Damn, I'm Good" difficulty.
Burn 50 bad guys to death.
Find Luke in the Level "Lunar Reactor"
Kill 10 bad guys in 10 seconds while on steroids.