This can be done simply, by going offline and racing the AI cars. Pull out your Ethernet Cable/Wireless Adapter.
First of all, make sure your stake amount is set to $2,000 as the AI cars won't accept anything higher.
Hit then go to "Options". Go down 3 and select "Game settings", at the bottom you'll see "stake". Select $2,000. Now make sure you hit and not so it will save.
Now find an AI car, make sure you're driving a faster car and flash your headlights and hit again to accept the stake. The AI car will accept and all you have to do is beat them 5 times in a row and the achievement is yours.
Alternatively you could up your Stake amount to $10,000 or greater and flash your lights at another racer and try to win if you'd prefer not to race 5 times.