Perform 1000 explosive kills. The quickest way to get this achievement, is to set up a match with the following settings:
Mode: Team Killcount
Map: Old Town
Map Size: Small
Bots: 15 (Agent) 14 on your team, 1 on the other
Weapons: Custom (Multi-Mines)
When the match begins, run through the teleport, turn around, then throw mines at the teleport exit. The aim is to kill your teammates, as teamkills count towards the kill achievements. Stand on an ammo box and keep throwing the mines. The 1000 kills will take a little over an hour using this method. It can be a mix of online and offline.
If you own a second controller, you can get your kills even quicker. Change the bots to 14, to allow for your second controller. Their personality needs to be set to "Bully". Also, add a Combat Shield in the fifth custom weapon slot. When the game begins, get into the same setup as "1000 Headshot Kills". Constantly throw your mines in the doorway entrance. Be careful not to walk into the blast radius of the Multi-Mines. You can kill 40 bots every minute, so 1000 explosive kills will take 25 minutes.
*You must complete the match for your achievement progress to register.