Simply put anything interesting or creative way to obtain these achievements.

I have: Hot Potatoes - Kill at least 3 or more zombies with each grenade you've thrown (Doesn't count with propane tank, you start with three grenades whenever you pick them up)

Classic Uppercutter or Sucker Puncher - Deal maximum damage with your fists Charge up your meter to max with your fists and then punch zombie / enemy bandit or enemy player Maybe also simple reference to Mortal Kombat?

Prescripted with pain - Deal 1.000.000 total of damage (Overall damage in your plays)

Western Cowboy - Equip the Winchester and Dual Revolvers (or even fully deplete them to fully count)

Risen Justice or Risen to Pacify - Kill bandits to be free As a zombie kill 3 bandits without dying and return back to human again

Kung Flu Fighting - In a single life, kick 25 zombies to death, punch zombies to death 20 times and uppercut 15 zombies to death (Dying will reset the counter)

Propane and pro-pain accessories - In a single life, explode propane tanks 5 times by your own hands (Resets if you die)

Healing Addiction - In a single life, heal 10 times (basically hoard medkits) or In a single life, heal 500 points of health

POSTAL Inception - Play as the POSTAL dude and get at least 20-25 kills with every weapon possible (excludes melee weapons and dualies) Referencing to the very first POSTAL game, you have to use grenade and revolver kills too or revolver one can be excluded cause it's in Redux version

Oh Hi Fred - Kill Fred in less than 45-60s (Reference to The Room movie, horrible movie? Horrid challenge / achievement)

Situation Under Control or Prepare to be De-Terminated - Kill 5 zombie players in a single life

Deus Ex Schmachina - Kill 60 zombies in less than 60s

Your hurting angel or You're going with me! or Happy Ending - Pull the grenade pin and find peace with a zombie player

Speed Limiter - Have 2-3 seconds of airborn time Sliding ability is your key

Crimed'n'Robbed - Kill bandits and steal their weapons 10 times (Overall plays)

You're too fast! - Finish all of any map objectives (on objectives only obtainable) in less than 5-10 minutes Obvious Sonic the Hedgehog quote is obvious

For Science? - Complete any objective / survival map whilst crouching (You can shoot and defend yourself of course)

Sweeper - Kill 3 zombie players with headshots only

Open Shift - In Mecklenburg objective map defend off zombie horde from the Gun Store while neither you or your partners die (once this event ends and you all survived the achievement should pop)

Mazel Tov - Get 69 headshots in a row (can work with bandits too)

Zombie Acrobatics - Finish off Fred while he's jumping (or if willing to make this harder do this with melee weapon)

Wrecker Ball - Kill a zombie player with a sledgerhammer Miley Cyrus reference from music video Wrecking Ball

Factory Genocide or Factory Dweller - Killing 20-25 Bandits in Compound objective map and escape safe and sound without killing any zombies

Quarantine Backlash or Quarantine'd - In Mecklenburg Objective map secure all of the apartments in less than 5:30-6 minutes (or lower)

300 or This is Sparta! - Kick enemies (both zombies and bandits overall count) to death 300 times with kicking ability. Or even do this many kicking ability kills in coliseum survival map specifically.

Brick Shatter - Kill a zombie player by throwing a brick at them

This is better than Jumanji - Kill 1995 enemies with a machete in the Swamp survival map (both bandits and zombies count overall respectively)

Melee Hat Trick - Joggle and kill at least once with three melee weapons in 20 seconds

HIDDEN Achievements

Math is cool - In Mecklenburg objective map, calculate a chest in the Police Station (It's keypad related)

Don't bring legs into a gun fight - When in doubt of losing ammo, whip out the high kicks. (One enemy is all you need)

I may add more ideas if they come by, feel free to fill up more ideas below!