Me and a bunch of fellow gamers followed LSDintensity's boosting method strategy with some modifications of our own based on our own experiences.
1. Boost this achievement in the early morning hours on the weekdays and weekends (6 am - 9 am Pacific Time / 9 am - 12 noon Eastern Time / 2 pm - 5 pm Greenwich Mean Time (UTC)). You'll deal with less random and modders.
The later you play this game - the more headaches you'll have fighting off the randoms and modders (ridiculous speed, near-infinite health, unlimited ammo, and gold chains).
Don't boost this achievement between 6 pm - 12 midnight Eastern (GMT - 5), everybody plays during that time and you'll be lucky to get more than a couple of pimp kills.
2. Search as two different private parties (groups) to keep all your boosters together in the same matchmaking lobby.
If you got a second console and copy of the game, you can use it to run interference to start a more heavily populated game to clear space for your boosting match or get your odd-numbered game started.
Otherwise, one party does a quick look to see if anybody is in a lobby, while the second party wait for the all clear to join the other party in the matchmaking lobby.
If for some reason, you get a even number of people including one or two randoms, that's ok. Develop a quick strategy on how to beat the randoms for a pimp kill. If necessary, team killing the randoms is justified. Just remember, the random(s) will be looking for revenge during the next round and the rest of the match.
3. You should do it 3 vs 3 to maintain an even balance of kills among boosters. Not to say 5 vs 5 or 6 vs 6 isn't doable - but not everybody got a second console and copy of the game. You can do 2 vs 2 as well, but it takes at least a couple of minutes to start a match and the random/modders will appear out of nowhere and fill the lobby.
Be mindful that odd-numbered matchmatching lobbies can cut off a random and/or a group of players more likely than not if you got six or more players waiting to start a match - so patience could work in your favor.
4. If you have trouble connecting the two parties to each other, change party hosts depending on geography does help. For example, two party hosts that are in New York City and Chicago got a better chance connecting than party hosts in Los Angeles and Moscow.
5. For this game type, Protect Tha Pimp - you got three levels, Airport, Hospital, Record Building.
For the hospital level - three levels exist (if the walls are red, you're on the top floor, blue is the middle floor, and green is the bottom floor).
For the record building level, the penthouse is the top floor, the cubicles is the middle floor, the cafeteria/entrance is bottom floor.
The airport is based on the distance, so the closest you are to the main escalators, the closer you are to the pimp you need to kill.
Have the hitmen team call out which floor/position they're on. It will reduce the time needed to get pimp kills and end the match by knowing who's closest to get the pimp kill. The pimp always spawn on the top level (except for the airport level, the pimp is farthest from the exit).
With luck, a 3 hour session can get you between 10 - 20 pimp kills. Good luck with the achievement, you'll need it. Any questions, please feel free to ask.
A special thanks to the original creator of the solution: LSDintensity.
Additional thanks for twitchinmonkey, ShimmeringCube, Delta381, Ray Jerkins, Mindful Force, Super Erik NL, Zogias, SebVin, My Name is BaRt, IX iC0n1k XI and everybody else who participated in getting this achievement with me.