Hot Potato
25 
Pick up and return 5 live grenades.
This must be done during one level, not over the course of the game. There is a balcony in the top floor of a house where you end up on the first level of the game, and you are charged with holding the position with your comrades. Stand at the balcony and enemy grenades will be thrown at you. Simply throw them away and you will recieve this achievement.
An easy way is to throw five grenades on the ground and then pick them up and throw them.