"The only woman I'm pimping is sweet lady propane! And I'm tricking her out all over this town."
This could very well be the hardest Challenge in SSO, if only because part of it requires you to be lucky.
First of all, you are going to need to get the ProPain Launcher. But you can't just simply BUY the ProPain launcher like any other weapon. No, you are going to need to tackle Chaos Squad.
Chaos Squad is a short multiplayer mode where you and several others do all sorts of wacky challenges in order to gain Chaos and boosts for a Night Defense at the end. There are two bonus individual challenges for said minigames that will get you either a 2x point multiplayer or a 4x point multiplayer per challenge if completed. All this culminates in a Night Defense, and if you win, you get extra points based off whatever percentage of Chaos you obtained. After all this, the game plays a spinner for you.
You get one free slot and four more slots that you can unlock based on how well you did in Chaos Squad. The free slot normally gives useless things like weapon boosts. What you are aiming for is to get the four score slots. The bigger the slot, the better the reward. The ProPain Launcher is the rarest Chaos Squad reward and most commonly drops from your Fifth Spin, though it is possible to get it on your third spin. Some people might get this on their first round of Chaos Squad, some might plays dozens of rounds and not get even a hint of it. The easiest Chaos Squad mode for getting all five spins, in my opinion, is Little Tokyo.
Once you get the ProPain Launcher, you now have the delightful task of hunting down Spawners. Spawners are Special OD that have a dumpster embedded in their back that normal, boring OD crawl out of. Spawners are cowardly and will run away when faced with violence, so you might have to give a chase. It is not recommended you get close to the Spawner, as they have a brutal melee attack.
Spawners seem to be a rather rare creature to find in the wild, but they are either dormant or moving extremely slowly, so look for slow moving or stationary big red dots on your minimap. After that, nuke it with the ProPain Launcher. It'll only take two shots (and that's without a single upgrade!)
There is a guaranteed Spawner location. From the mission selection menu, select To Cure a Case of the Scabs. Right at the start area, you will find a Spawner that is fleeing for his life. Kill it with your ProPain launcher, restart the mission, do this ten times, and the achievement should be yours! You shouldn't worry about ammo, because if you hit the Spawner right in its ugly face, it'll only take two shots of your ProPain Launcher, and the starting ammo capacity is 26.