Step by step:
This is obtained in episode 2, "Moai Better Blues". First thing you do in the chapter, before it's too late: Order "Today's Special" at Stinky's and get the granite sandwich.
Then: Immediately after entering the Easter Island the first time, start offering the sandwich to everyone there. These are the people you have to "use" the sandwich on:
Sybil, Abe Lincoln, The Three Moai Heads (each one separately), Baby Huffa (the one with the gun), the three babies, baby Glenn Miller
As already stated by "mik29" and "KMetalmind" you better do this achievements as soon as possible because afterward in the story progression some characters might disappear.