"Bayheimer - Cool guys don't look at explosions: This achievement can be earned by killing an enemy pro with explosion damage with your back turned" Can the explosion from the summer costume taunts kill?
I got this at some point the night the Summer Camp Sale started but I didn't notice it at the time so I am not sure exactly what triggered it. The general understanding is killing someone with an Assault bomb or Support airstrike while they are not in your field of view. It may be possible to trigger it with the Grenade Launcher or Mortor since it says "Explosive Damage" but I don't know. Easy enough to get with airstrikes though since they are fire and forget, and will kill even if you don't stick it to the target. Sure you can run but with all the newer players playing at the moment I am sure one of them will not get out in time XD.
I just got this. All you need to do is get a kill or assist with either assault bomb or support ground zero when the target is not in your field of view. It actually incredibly easy to get and you'll probably get it by accident if you play 4-5 matches.
Pretty much what Ino said. I got the achivement on my first run on GrenAde III arena. I would go for support for this rather then Assault. Unless you play Assault enough to pull off headcrabs like a beast.
I take it the Assassin won't be joining in this party? She's kind of non-explosive, except for her poof clouds. :|
Random airstrikes are amazing for this, that's how I got it. Chuck a random airstrike go do other stuff like heal or repair turrets. Get Achievement.