Randy read the temporary transformation aging Jeff to adulthood. Enraged that again he is going to be submitting a report about a magical device that causes temporary chaos, but its okay because it fixes itself later.
Flipping over to Jeff's mental attributes, the officer saw Jeff was mostly irritated that he wasn't getting to try adult things now that he was temporarily an adult an was frustrated he was naked and without cash to check out a bar while he waits for things to die down.
The kid didn't care about the panic he caused his dad, the fact that he mobilized the whole town's police force for a missing kid, or that all the neighbors are getting knocks on their doors about a naked man and missing boy... inexcusable.
This was not what Officer Randy had in mind when he joined the force, and to make things worse Jeff is just going to walk back into his life and get away scot-free, mindless of the effects he has on everyone. Anything the officer could do like a ticket for wasting city resources would fall back on Mike. Randy decided to teach Jeff a lesson.