Rob,
Fair play to you for trying to sort out these herbert's. I try to educate them when i take them on their CBT's that they will be frowned apon when they are out and about in groups hanging around street corners making a pest of themselves, it just seems to go in one ear and out the other.
This time of year is worse as the days are longer and the weather is warmer, which makes them believe that they are "Road Proof" as most of them now wear nothing more than a tee shirt. I believe that if you could show them some photos of what "Road Rash" looks like or photos of accidents then this might convince them to ride a bit safer. I know it all sounds a bit gorie but it might be the evidence and proof that they need, plus also teach them Etiquette when riding in groups. If you needed a hand I would be willing to help "Work Permitting"
Short of that give them a good Slapping
