I appreciate your concern for the guy I was pasting... but given your detailed reply, I feel as if I should provie a detailed answer to those who don't understand UK/Aus banter.
Between me and the guy I replied to (who is most likely the ancestor of some east London criminal)... he clearly understands that I am a Brit. And when British people refer to Australia as a prison colony it is meant purely in jest. And both cultures understand that without taking actual offence. As do they not take offence when we refer to one another as "cunt" because any true Aussie knows that "cunt" is actually a term of endearment. Much as it is in the UK (if only to a lesser extent). So to an outsider I can understand how this banter may be misunderstood as harsh xenophobia... it's not, in fact it's the opposite. Because Brits & Aussies/Kiwis understand each other far better than the mysteriously overdramatic American.