Here is the full list of all 13 Definitely Sneaky But Not Sneaky achievements.
Complete the first level
Kill an enemy
You died
Complete the first difficulty mode
Complete the second difficulty mode
Deflect a bullet
Kill a teammate
Buy a mod in survival mode
You have exploded
Buy a weapon in survival mode
Blow up 5 enemies with 1 explosion
Blow up 10 enemies with 1 explosion
Blow up 25 enemies with 1 explosion