First of all, you'll need regular, very decent income.
Next go to a gun shop and upgrade your stun grenade to four, which turns it into "Fart in a jar".
If you upgrade your grenade capacity, this trophy goes alot faster. Carrying 6+ of them at a time, make this a doddle.
Make sure to equip "The penentrator" as your Melee weapon and get ready for fighting. I personally found that Deckers were easier to fight using this method.
1) Find the gang operation to the west of Burns Hill (although any in a large close group will suffice). Throw an Fart in a jar at them then get in a decent position to equip Penentrator.
2) wait for them to stop throwing up and hit them with a second Fart in a jar.
3) clear the operation using penentrator.
4) You may still need more. Use the back up to boost and if you still don't have it.
5) Hit another Gang operation. Trophy should pop at this second site.