Grand Theft Auto IV: The Complete Edition

Got the achievement using this method in the "first date" mission. I always do two steps to the left and then gently move mouse. I don't know if there is a better way but this worked for me.

During a bike race hold left/right click and hit one of the bikers. Park up next to them and as soon as they get back on their bike hit them again.
It took me a couple of races to do this 69 times and some time to get the timing right so they don't ride away.