Who's driving the boat?
At the end of the film, Liam has killed a whole boatload of kidnappers, but the boat remains on its course, moving at quite a pace. One would imagine that any boat captain who was aware of the relentless slaughter happening on board would try to escape. Liam himself doesn't seem to want to investigate the bridge. If the boat is not being driven, it is going to crash!
The line has also been used to describe other films in which narrative holes are obvious.
The phrase was graffitied underneath a poster for the film near London Bridge station, something Mark described as "wonderful".