Next time take a deep breath before telling another pilot off.
Telling off in an abusive manner maybe a no-no, but it sure as hell it sounds like a stern and straight conversation was required.Imagine the PPL'er had gone home none the wiser?
He needed to hear the danger he had placed several people in. If he heard it in a strong yet non abusive manner, then good. He needs to suck it up.
If too many people stay silent, and dont tell or "dob" in other pilots, then who knows how big the holes get in the "swiss cheese" over time..
I bet this pilot will never again transmit on the wrong freq..