It is well known that Britain had the largest Empire, and from a nationalist point of view: the best. I honestly don't care about what "wrongs" we committed as it made us great, and often it is the ruthless who come out victorious. But like all empires, the British eventually crumble, but its legacy remains. God save the Queen!
Americans might argue that they left the Mother Country in search of more freedoms, but in modern England there are more freedoms than there are in America. There is a lot to be proud of when it comes to being British, but one thing in particular is that British people use science and reason more than religion.
As an American I can not honestly say I am not proud to be British. I am proud to be part of my country though. We may make mistakes, and sometimes step on the wrong foot of others, but overall we try hard and do what we can for others and that is what counts.
Don't get me wrong, I don't dislike Britain - I'm happy I was born here. But proud of being British? No. I don't see why I would be proud about an accident of birth that had nothing to do with me. Just like people today being proud of the former British Empire is stupid, as you had nothing to do with it, no involvement whatsoever. And the royal family are benefit scrounging scum bags.