Motorcyclists in London generally have personalities which fall somewhere between Adolf Hitler and Genghis Khan. I know there are exceptions because, one day, I met both of them.
By far the worst of the breed are young hooligans hired to "aim" pizza delivery scooters around the streets and very high speed and with complete disregard for other road users.
In the Clapham area, the worst of these work for Basilico on Lavender Hill. I am still not sure whether the delinquents are hired specifically for their lunatic driving or whether the company has a training course to make sure that the pizza remains hot to the table no matter whom you might kill on the way.