Cyclists signalled their frustration at Boris Johnson as he arrived on his bike to open a new cycling super highway in London.
Some shouted abuse at the mayor and one made a rude gesture in his direction.
The route, connecting Vauxhall to Oval in south London, was hailed by Boris Johnson as a "wonderful thing".
The London Cycling Campaign welcomed the new route but acknowledged some cyclists are "frustrated" with the pace of progress.
The new cycling "super highway" introduces two dedicated lanes for cyclists on Vauxhall Bridge, separated from cars and lorries by a raised concrete partition.
Mr Johnson admitted it was "one of the most difficult things we have had to do" and "has caused an awful lot of aggro, particularly with senior colleagues in Parliament who like to travel around in cars".
Simon Munk, of the London Cycling Campaign, praised the mayor for taking "big steps in the right direction" but said other "so-called" cycleways painted on the road had made some cyclists "incandescently angry".
"They are frustrated with the pace of progress, and that's telling us there's still some way to go to catch up with the best models in Europe."
Work on the route began in April and was carried out in stages, causing road closures and traffic delays.