Good guy cop

Nope, sounds like a burn.

But how does the police know he was hooking up with a girl (unless he told him)?

Well I guess he told him. They usually ask you where you're going.

Maybe it went something like this:

Cop pulls kid over and steps up to the window as he hitches up his belt.
Cop: Whar's the fiaar boyh?
Boy: In my girl's eyes...
Cop: Well dagum son, dat raight thar was maighty smooth. Teel yew whut, ai'll leet yew off thees taiym, but yew best slow it down, y'heah?