Race Pro

for this you just need to race in 50 ranked matches. best to do with a friend. you can reverse during qualifying to speed it up also do 1 lap races( you can change this in the settlings)
achievement unlocked

Okay, just want to add a few things to the solution Superschrubber made. So play Curitiba, F3000 cars, drive into the pit the wrong way or on the track for an amount of time to get disqualified, then race.

First of all, when you are boosting this in the way he stated, make sure that you both finish the race!!!
When you finish, it will count toward your "complete" achievement. But only when the other finishes it will also count towards the "finish 1st & host" achievements.

Second, this is going to take a very long time... you can average about 10/12 races in one hour. But with a 100 races to play till both get the achievement... don't fall asleep ;-)