For those of you who do not understand the achievement, you must tag a grenade to an inanimate object (by selcting the grenade and press B) and get an enemy to walk into it blowing themselves up a total of ten times.
Set up the campaign on the chapter 'tip of the spear' part 'road block'.
You will start by joining Tai after he comicly removes himself from a blown up vehicle.
Head straight into the store on the left as per normal progression and go up stairs to get all the ammo you need including some frag grenades.
Once you are finished, go back downstairs and continue through the hallway where 'Tickers' are introduced. This will in turn activate a check point.
After this little description of them, roadie run to the end of the hallway and turn right towards the door frame leading outside and tag a frag grenade to the outside of this door frame.
Run back inside and watch as tickers walk into your convieniently placed grenade! Repeat the above with your remaining grenade.
Once your out of grenades, either pause and reload your last checkpoint or just blow yourself up next to a ticker to restart. You will restart with all your grenades and your achievement counter will remain at how many you've just blown up!
It took me just two restarts and was so easy to do as the Tickers MUST get through that door way to get to you! If your lucky, you can blow up three tickers with just one grenade!
I did this on insane difficulty but you can pick whatever difficulty you like.
After just one or two minutes, that's achievement unlocked!