Can civilians enforce traffic laws?

First off, let me say, I am a very conscientious driver, and I rarely go more than a few miles over the speed limit, and have never had a ticket in 8 years of driving. I was driving on the highway today, and coming up towards my exit. There was a red Ford Focus in the lane I needed to be in to exit, driving right next to me. I tried to speed up a little to pass him but he sped up too, so I tried slowing down to get behind him in the lane, and then he slowed down! Clearly this guy was being a jerk, and I needed to get in that lane soon or I'd miss my exit (the next exit was about 10 miles down the high way - really didn't want to have to drive that far to turn around) so I sped up to about 80 mph - the speed limit was 65 mph - and I passed him and got in the right lane. Well, I looked in my rear view mirror and the guy had his cell phone out, either taking a video or a picture of me! Then, he switched lanes and pulled up next to me as I was getting onto the exit ramp, and took another video/picture of me when I looked at him! It looked to me like he was getting my license plate number and a picture of my face. My question is...why would he do this? I admit that I DID speed up to pass him, and I guess technically that's breaking the law...but as a civilian, can he do anything about that? If you catch someone speeding like that and you get their license plate and a picture of their face, can you report them to the police to get them ticketed? If he'd been an unmarked cop (he wasn't because they all drive crown vic's here) then he'd have just pulled me over, so I assume he had to be a civillian. And if he's not reporting me to the police, what would he be doing with a picture of me that he clearly took without my permission?