Credit to Foerl on TrueAchievements.com:
- load up the level "Collapse" on easy
- after the driving sequence (1-2min into the level) run forward
- enemies will jump on trucks - the left guy on the right truck will always throw a grenade
- dodge the grenade (red indicator) by clicking your left stick in either right or left direction
- reload last checkpoint - run forward and repeat.