Aliens Colonial Marines

Here is a good place to do this. During the first level you will come through a door and see 2 enemies coming up on the right side. Cook a grenade a few seconds before they get up and toss it at them. If confused then look at the video below. The checkpoint is right before you go through the door so if you fail then restart to that checkpoint.

Equip a grenade by press left on D-PAD.

This isn't necessarily a solution. I just wanted to add that you can do this very easily in the multiplayer. If you play extermination and go to capture one of the objectives just place a claymore at your feet. More often then not 4 or 5 aliens will swarm the objective trying to kill you and your team mates. Popped this my first game.

I got this by getting a double kill using the assault rifles grenade launcher attachment.
I did this on the first level.
Good Luck, and happy hunting!

NOTE: Must have the bodies with explode into pieces, not just be killed by the explosion.
Hope that clears things up.

RPG works too..

I didn't get it early on, and put it down as something to mop up later, but got it by chance later on in mission 10.

Mission 10: Derelict Reclaimed sees you getting the RPG to destoy the AA guns, you can't re-load it, but if you switch back to primary weopen after destroying the AA you can pick it up again to use as you move on to the next gun. Simply pick up the RPG again and then use it against the next group of targets, be they WY bad guys or Xeno's.
Mine was WY folks as they don't move around as much and as fast as Xeno's

One of my friends in a boosting group got this achievement by mistake. We tested it out and it actually worked. There is a glitch you can do to get this achievement, and... it's actually quite funny.

When playing multiplayer, simply get the person who wants the achievement to play as a Marine and equip the Grenades with (). Make sure they have the Grenades equipped in one of the 5 classes available for you to choose from. Get an Alien on the opposite team to come over and stand nearby them. Now the person who has the Grenade aims at the floor and then throws it with to let it bounce and place itself onto the ground. Get the Alien and the Marine (yourself) to stand nearby the thrown Grenade.

The Grenade impact should kill the Alien, but will also blow the Marine into pieces, counting as a suicide... Achievement Popped!

Yes, you as in yourself count as an enemy towards yourself in this game. Meaning that you can simply just blow yourself up with an Alien and you, yourself will get the achievement. You can't do this glitch though with another Marine, it only seems to work with 1 Marine and 1 Alien.

Credit goes to my friend TRACKEY for discovering the glitch.

At any point during campaign when multiple xenos attack (like in mission 1 when you have to defend yourself in the ship hall while Keyes unlocks the door) hold Y, select left and equip your claymore mine, have the xenos gather in front of you, then plant the claymore there on the ground, and boom, achievement unlocked.

RPG works too..

I didn't get it early on, and put it down as something to mop up later, but got it by chance later on in mission 10.

Mission 10: Derelict Reclaimed sees you getting the RPG to destoy the AA guns, you can't re-load it, but if you switch back to primary weopen after destroying the AA you can pick it up again to use as you move on to the next gun. Simply pick up the RPG again and then use it against the next group of targets, be they WY bad guys or Xeno's.
Mine was WY folks as they don't move around as much and as fast as Xeno's