Here is the full list of all 40 Destroy All Humans! achievements. It takes around 10-12 hours to unlock all of the achievements on Windows.
Demonstrate Furon free spirit near a warning sign placed by the human authorities
Set something on fire, then use it to destroy a hapless human
Complete all optional mission objectives! (Use the Holopoxdeck if you have to.)
Destroy humanity's last hope and initiate the subjugation of the species
Destroy the pathetic human attempt at a robot overlord
Abduct and drain a vehicle to replenish your saucer's shields
Ace all challenges!
Display Furonic aeronautic prowess by soaring through giant human pastry without soiling your feet
Destroy a certain irritating simian warlord once and for all
Invade Capitol City
Invade Union Town
Accelerate Brain Extract or Transmog by mashing that button like you mean it
Throw a human into the air and juggle them
Obtain at least a two-star rating for each challenge type
Ace an Abduction challenge with a three-star rating
Ace a Race challenge with a three-star rating
Fully upgrade one of the branches of a weapon or ability
Ace an Armageddon challenge with a three-star rating
Abduct a cow with your saucer
Invade Area 42
Evade a rocket by dashing
Explore the more offbeat parts of the mothership
Try out a new look for Crypto in the mothership's archives
Use your saucer's Repulse-O-Tron to fend off homing missiles
Upgrade your saucer at Pox's Lab in the mothership
Transmogrify an object to replenish your ammunition
Invade Santa Modesta
Re-visit a mission in the mothership archive's Holopoxdeck
Revisit a missionless invasion site and complete a challenge there
Ace a Rampage challenge with a three-star rating
Destroy a human with a weapon and another with a psi ability at the same time
Upgrade Crypto at Pox's Lab in the mothership
Destroy multiple humans with a human-made explosive
Throw something into something else with the saucer's Abducto Beam
Stay covert by scanning primitive human thoughts
Invade Rockwell
Recover a Furon Probe
Use PK to destroy a human with another human
Consume a human brain to kickstart your shield regeneration
Invade Turnipseed Farm