You must destroy 300 destructible objects. Very easily done on Level 8. It will take about 1.5-2 playthroughs of level 8 to do this. Almost anything can be destroyed from fire extinguishers to electrical boxes, to chairs to laptops to TV's etc. In the level there will be a massive fight in an office area, there will be tons of offices on the main room and in side rooms with plenty to destroy (laptops, chairs, clocks, TV's) and then there will be another fight in Dalton's main room before the vault where you will be a huge screen with Tyson and Rios' face on it. That huge screen has 48 individual screens which can all be destroyed. There is nothing more to really say for this achievement though, just shoot anything that looks like it can be destroyed. You can also find an area, destroy everything than die and come back and keep rinsing and repeating. But after a maximum of 2 playthroughs of the level destroying everything you see you should have it. I got it in 1 and a half playthroughs. It unlocked on my second playthrough in the massive TV room with Tyson and Rios' face on the screen. Oh yea and also if you are doing co-op you must each destroy 300 objects, you can't get 150 than have your partner get 150, each person must destroy 300.