Here is the full list of all 10 Operation: Cheek Clapper achievements.
Clapped the first alien cheek!
Clapped 10 alien cheeks in your lifetime
Clapped 25 alien cheeks in your lifetime
Clapped 100 alien cheeks in your lifetime
Clapped 1000 alien cheeks in your lifetime
Execute the fabled backhand clap
Clap two alien cheeks in one warp clap
Knock out 7 soldiers in one Kyle's Charge
Warp to an alien above you
Knock away an alien