UPDATE: Server shut down, achievement unobtainable.
You'll most likely need to boost this. Here goes:
1) Get a party together of 6 people including yourself.
2) One person create a lobby. Change Ranked to "No". Change Laps to "1". Change Rounds to "1". Change Security to "Private". We had a little problem getting everyone to connect, so you may need to play around with who hosts the lobby.
3) Pick any track with the word "Short" in it. Once the lobby is up, invite the party and everyone ready up.
4) Decide who will get the achievement first. That person must takedown all other racers. The markers next to each person's name must be GREEN. Red will NOT work. Once this player gets all green markers next to the names, that player should finish the race in 1st (that's how we did it; comments say winning isn't required). The achievement will unlock FOR THIS PLAYER ONLY when you get back to the lobby.
5) Start the race back up and repeat the process for the other players. It should take about an hour.
Thanks to the people that helped me get this achievement, III JONESY III, TJHanson (and his two copies), xvd4ever, and DemonATX1337!