It's All In The Reflexes Bug

Copied from a post back in the CTA because this still exists:

Sandstorm says that you have to throw back an enemy's live grenade and get a kill in order to get the achievement. I, however, got the achievement by:

F*cking up a grenade
Picking up my own grenade
Lobbing it at a bunch of hostiles
I got at least one kill and got the achievement. Either the description needs to be updated or the achievement needs to be modified so it only triggers on enemy grenades.

It probably triggers if you simply pick up any grenade and get a kill with it.

On another note I haven't gotten the MVP achievement even though I've been at the top of my leaderboard many a times now.