You get this achievement for being "crushed" by a large enemy. There are multiple opportunities to get this throughout the game, but the earliest point is in SKY CASTLE level HEAVY HEADS.
From the beginning of the level, go straight and talk to Mew-Shu the cat. After he 'vanishes,' go through the open double doors and tail whip (
) the sad-face sign on the right. Continue on and you'll hit a checkpoint and a disembodied head will start a conversation with you.
Ignore him for now. Instead, go left, past the L in the cage and the annoying bee, until you reach the island with a face totem with flames in its mouth. In front of the totem, you'll see a glowing portal with a spinning lid. This is a fox hole. Stand on the lid and push
to enter the fox hole.
After Mew-Shu vanishes, a giant flower will appear. Stand directly in front of the flower and it will hit you. After you're hit once (it doesn't need to be your last heart), the achievement will unlock!
Note that the normal flowers throughout the level aren't big enough to "crush" you. It must be the large flowers in the fox hole or some other large enemy.