You first get the sticky grenade after surviving the first part of Chapter 6. After you meet up with Lugo and Adams again, three guys kick down a little bridge. Behind these three is a box containing the sticky grenades. Kill the first two guys (who usually run straight down the bridge) but melee the third guy to the ground. Then go pick up the sticky grenades behind him and while's he's lying on the ground waiting to be executed, throw a sticky grenade on him and once he stands up and runs towards you, the sticky grenade will blow him up and you'll get the achievement.