Here is the full list of all 21 Poop Slinger achievements.
Pooped on a Chicken
Pooped on a White Duck
Pooped on a Bucket
Pooped on Popcorn
Pooped on a Boom Box
Pooped on a Toolbox
Pooped on a Brown Duck
Pooped on a Cooler
Pooped on a Pig
Eliminated 250 Joggers
Eliminated 250 Bikinis
Eliminated 50 Tourists
Eliminated 50 Hobos
Eliminated 50 Top Hats
Eliminated 25 Prisoners
Eliminated 25 Robbers
Eliminated 25 Thugs
Eliminated 5000 Citizens
All Poop Colors Unlocked
Eliminated 10000 Citizens
All Slingers Unlocked