Here is the full list of all 10 3..2..1..Grenades! achievements.
Kill a player who is in the air with a bullseye
Kill one bot
Assassinate a player twice in one match
Assassinate a player that assassinated you.
Kill 100 bots
Collect 10 golden grenades
Collect all 90 golden grenades.
Get a Mega Kill Streak (5 kills in a row without dying)
Get a Grenade Master Kill Streak ( 10 Kills in a row without dying)
Get a Rampage Kill Streak (8 Kills in a row without dying)