I agree completely with Wilmo X's solution (right down to the timing), and Evil Demon55 wrote a great badge guide for x360a, but for some reason the order of the guide was difficult for me to follow, so I reordered the list and made some of my own notes, original list is here: http://www.xbox360achievements.org/forum/showthread.php?t=97...
Again, all credit goes to Evil Demon55 for the original list
You can check completed badges in Multiplayer>Xbox LIVE>Player Customization>Wardrobe>Badges.
Match Related Badges
1. Arr… - Play a multiplayer match on September 19th (International Talk Like a Pirate Day) or December 5th (Day of the Ninja).
2. Party Animal - Host and win 1 Party Lobby.
Host a party match and win it.
3. Wrecking Crew - Earn over $50,000 lifetime earnings in Mayhem and/or Demolition Derby.
Set a Strong Arm game to $100,000 and turn off everything but Mayhem. Make sure to have unlimited ammo. When the game starts make sure you have pipebombs and a rocket launcher. Go to the location and throw pipebombs everywhere. When luxory cars start to show up, blow them up with the rocket. You will make $50,000 in less than 10 minutes this way.
4. Regulator - End 5 matches with over $30,000 in personal earnings.
Make a Strong Arm game and set the score to $50,000. Play the activities and win the match. Do this for 5 times. You will get this easily and quickly.
5. Original Gangsta - Play 10 ranked matches.
Just play 10 ranked matches, win or loose, it does not matter.
6. No Questions Asked - Play in 10 matches where you score at least 20 kills.
Just play 10 matches and set kill limit to 25 with unlimited time. With your partner, both get 20+ kills then finish the match. Do this 10 times and you will have the badge. Check the kills related badges to find productive ways of getting those 20+ kills.
7. Pimp - Play 20 matches.
All you have to do is play 20 matches. Can be ranked or custom/party. You will get this over time, and most likely get this while boosting for badges.
Killing/Dying Related Badges
8. Demo Demon - Drive 10 cars until they catch on fire, and remain in them until they explode.
To get this badge, you have to get someone to shoot your car until it catches on fire and drive off while your car is on fire and then you blow up in it. What I did was shoot my car until it had black smoke then got on a long street and had my friend stand halfway down the street. I drove slowly down the street and he shot my car, once it caught on fire he stopped shooting and I started to accelerate. I then just drove and blew up. Getting 10 of these will be easy.
9. Team Spirit - Kill 10 players with the pimp slap.
Get 10 kills with the Pimp Finger. The Pimp Finger is a foam finger with the middle finger up.
10. Burnout - Kill 15 players by lighting them on fire.
Use the flamethrower or Molotov cocktail to kill 15 players and make sure it shows the symbol of the weapon you used.
11. Road Rage - Kill 30 players with a vehicle impact.
Just be in a car and hit and kill other players who are NOT on your team. Make sure the kill icon is a picture of a car. 30 of these will not be hard at all.
12. Assault and Battery - Kill 30 players with non-pimp slap melee attacks.
To do this just make it show a fist when you kill someone on the bottom left part of the screen. To do that, hit when they are about to die, this will count as a bare hand kill. Make sure you have 30 of these, you might accidentally get some non bare hand kills, so make sure to count all 30 (Don't charge your hit, or hit from behind to avoid the scope kill symbol, which does not count as a melee kill).
13. Brain Surgeon - Kill 100 players with a headshot.
Get a sniper rifle and aim at the head and shoot and kill them. It is a 1 hit kill. You do not need the sniper rifle but it is recommended.
14. Nut Job - Kill 100 players with a nutshot.
Get a sniper rifle and shoot someone in the nuts 100 times. It takes 3 shots in the nuts to kill them. They will grab their nuts when they die, that will count as 1 nushot. Girls have nuts. You do not need the sniper rifle but it is recommended and you will not get the Aww Nuts! achievement for doing this.
15. Mass Murder - Score 10 Multikills (Kill another player within one second of getting a kill).
To get a multi-kill just kill 2-3 people in less than 1 second of the first kill. It may seem hard, but it really is simple. If you run two people over at once it will count as a multi-kill. You will get this by just playing online and in player matches.
Action Related Badges
16. Saint Picasso - Finish 150 tags.
You might not get this after 100 tags, for some people it has taken over 250 tags. Just have you and your partner keep re-tagging the same tag. Your partner has to be on the opposite team. Best done while going for "Leadfoot".
17. Trigger Happy - Empty 250 clips by firing continuously (1 trigger pull per clip).
During a party match get double semi-pistols with unlimited ammo on and keep shooting for about 15 minutes and you should get the badge after the game. Easy to get legit if you play online a lot. You must unload the full clip and make the gun auto-reload for it to count. Also pretty easy to do while you are getting shot in the nuts or the head, aim for the sky and squeeze the trigger.
18. Fully Loaded - Spend 300 seconds with all your weapon slots filled.
300 seconds is 5 minutes. When you press make sure every slot is full. You do not have to have dual-wielding. Really, really easy.
19. Leadfoot - Spend 1000 seconds racing in first place.
1000 seconds is about 17 minutes. During a Strong Arm game, the activity has to be Racing. Be in first for 17 minutes total and you will have this badge. Can be done in Party Mode, just make it so Racing is the only activity. Go through 1 checkpoint and you will be in first.
20. Track Star - Spend 6000 seconds sprinting.
6000 seconds is 100 minutes, or 1 hour 40 minutes. 100 minutes of sprinting is a lot. Turn on unlimited sprint and boost every other badge. Do not drive in any car just sprint everywhere you go. You should get this around your 15th badge.