This reminds me of the time two older, well-dressed cyclists and their dog were going the wrong way up a fast, curved, nasty one-way street in Whitechapel (Three Colt Street, by St. Anne's church, outside the old Wheelers workshop for those of you that know the area). I said "look out, you're going the wrong way up a one-way street".
Their response? "Nah, you're a mug, shut up!". I would have been glad to see a BMW take them out, to be honest.
Difficult to know what to do in these circs. I'd have made a judgement based on where I was, what he was dressed like, and how useful or otherwise my intervention could have been. By then I'd have been past him and thinking about whether I would still catch the 18.06 from the station, so I'd have carried on
