I did it last night on "warlord". The best way is to get/be inside the TV-Station. Just put some c4 on the Stairs/Wall and wait behind a corner upstairs for incoming enemy forces and blow them up. Its nearly impossible for them to get you killed, just watch out for those flashbangs. This might take some time, but it works...
City maps are the best for getting this badge. I got my basic in Sharqi, vet and expert in Karkand. Just jump and throw the C4 at the enemy, jump away and detonate. In time you will learn to do it right without getting the C4 bug (It drops two C4s instead of detonating). Also, try to be sneaky and get behind the enemy Oh, and by the way, try to get the badges before next patch
There was a topic called Fucking c4 badge, but I couldnt find it anymore. Yesterday I got a lot of c4 kills on Mashtuur City. As a MEC sneak into the enemy base where the choper lands. As those guys always are hanging out there and the choper always returns for a big repair. Just place those c4 explosives on the helipad and wait from a distance. I had 18 kills in 2 minutes. After that they knew i was in the neighbourhoud so it dinnt work anylonger. Give it a try i say
C4 Tossing/whoring is the way to go. Aside from that, find a big 64 karkand, load up a jeep with c4, and run into spawn points/choke areas and get kills. It's pretty easy.
If that doesn't work, play Karkand and put a few c4's on flags and wait for people to try to take the flag.