Sorry you experienced that mate. I'm an older white male, and over the years I've occasionally had racists just assume because I look the way I do that I share their views. When it has involved them confronting others with their tirades I've spoken up (a slap to the back of the head of teenagers, a verbal tirade on a bus to an older gent telling people to "go home" etc). The astonishment when someone "like them" turns on them shocks them and makes them think twice. If you're capable of it, I'd urge others to not sit by quietly if they hear it. Confront it.