playing through the game i've seen the steam achievements pop up from time to time and as I've been playing i've noticed some things that I think should be worth more of an achievement than say: giving another player your last ammo restock
so here's my list (which will be ongoing as I think of them) of things I think would be more interesting to have as achievments (add yours!)

"There's no 'I' in WELD"
As an engineer, repair a turret that has been hacked by an operative on your team.

"Oh no you don't!"
As an operative, hack a turret that has been hacked by an enemy operative. (if such a thing is possible)

"You think you're special?"
As an operative, kill an enemy operative that is disguised as you and then disquise yourself as them.

"Bigger is better"
As assault, place a sachel charge near an engineer's mine and have them kill an enemy. (you get the idea, like bad company 2 placing C4 next to an AT mine)

"Knife at a gun fight"
Use a pistol's melee knife attack to kill an enemy using a Heavy-type-only weapon. (minigun, hammer shotgun, ect)

"Brother against Brother"
As an operative, take manual control over an engineer's turret and use it to destroy an enemy engineer's turret.