Dave Grossman tells you that his secretary is ruining his life by claiming he sexually harrassed her. He wants you to intimidate her lawyer so she'll back off.
Grab a vehicle and make your way to Denver Avenue. As you approach, the lawyer will drive off. Catch him up and fire a few shots at his car to let him know you mean business.
If you're level with him when you shoot his car, that should be enough to scare him. After the cutscene you'll be rewarded.