Buy the "Rats" contract on Normal.
Day 1: Cook 4 bags of meth and make sure to get away with them.
Day 2: Take a loadout with shaped charges, and a bunch of armor. Load the 4 bags of meth in the truck, go up to the apartment indicated, but stop when you can see into the open doorway. There should be 2-3 gangers in the hallway, and 1 or 2 in the apartment. Kill the gangers in the hallway, move into the apartment and kill the gangers, then blow the safe. DO NOT ENTER the apartment before you start killing gangers, OR LOCKPICK the safes. Grab the money on the counter, the intel, and toss the money in the van, then grab the meth from the truck and put it in the van. The police should be arriving en masse at this point, so leave. Achievement should pop.