Complete all levels of Mayhem
In Mayhem, you will be given a bunch of weapons and a location, and you must cause a certain amount of money's worth in destruction before the time runs out. For every item you destroy, you will get a certain amount of money. If you destroy objects in rapid succession, you will get a multiplier bonus.

Your main target should be fences, as they go over easily and you get a multiplier credit for each panel you break. Anything else with similar qualities, like a outdoor dining area, will also do. Use grenades for the first two levels, and then your unlimited RPG for levels 3 and beyond.

There are 2 Mayhem activities with 6 levels apiece. I recommend doing this in co-op so you can work towards the "Confidence Men" achievement as well as "Crime Lord".

This achievement will reward 15G after completion.