Quick and simple achievement that can be obtained either with a second pad or online partner in a private match.
Set up a warzone game on Gridlock and set the boomshield spawn in the middle of the map next to the vans to frag grenades. Now both players meet there. The person going for the grenade kill will now have to equip the grenade and get hit down where they will get the option to blow the grenade which will kill themselves and the enemy player.
Easy as that