Y
Unless you stare at somebody's gender related body regions, every person must have the right to look wherever they may in a social situation free from judgement.
I don't think dealing with a cop working in his or her professional role really counts as a "social" situation.

As described, the whole thing sounds like, "He looked at me funny, so I followed his car, waited until he made a minor infraction, and then pulled him over for it to see if I could catch him at something worse. I couldn't, so issued a minor traffic citation, and made some ill-considered comments about how and why this stop happened."
Now, I can guess a cop can develop an intuition based on human behavior. Then, following to see if there really is something up makes at least some plausible sense. But, this guy was driving - so how much eye contact could he really have made? Did the suspect pull up to a stop-light next to the cop and stare like he was expecting to drag race, or something?