"Oh Shit" moments...

Because it's an additional risk that you're aware of and prepared to take when riding your bike simply by riding 'no-brakes'. This means you're also aware that you won't be able to stop as quickly as riding with a front brake. This means that by riding in this way you also pose an additional hazard to other road users. Simple really.

Indeed I am at greater risk, but I don't think I should just accept that this retard didn't signal or look in his mirrors and isn't aware of surroundings, so there is nothing I can do!

Mate....you need to learn how to stop the bike quickly/efficiently before riding brakeless, its as simple as that, if you can't skid (or equivalent method of stopping quickly) then put a brake on....or two, otherwise incidents like this will end up occuring frequently, and one day it will be more than a bruise.

Advice heeded, I'll get a front brake and and get to skidding today.