The activity is commonly known as door surfing.
Mr Mansill said the woman driving the car told police the pair wouldn't listen to her and get back into the car.
Both men received $150 infringement notices.
"But those fines could have been the least of their worries. You know, their behaviour at this time of year is pretty selfish," Mr Mansill said.
"While police are paid to be out on the roads at this time, this part of the Waikato is serviced by volunteer ambulance and fire crews and these dedicated people have to give up their precious family time to deal with this type of idiotic behaviour.
"I think when these two lads sober up they might want to spare a thought for the potential consequences."
Mr Mansill said the men's behaviour was "at the far end of the scale" and the majority of motorists have been well behaved.
"Traffic flows coming out of Auckland and into the Waikato have been very heavy and colleagues across the district are reporting big numbers of vehicles heading towards the Coromandel and Raglan," he said.
"Our message is to watch your speed, your following distance and keep within your lane and that way we'll all reach the beach in one piece, after all road safety is everyone's responsibility."