... Well, It's a reference to the Boston Tea Party
(in 1773, when Sam Adams and the Sons of Liberty
dressed as American Indians and boarded 3 British merchant ships and dumped their cargoes of tea in Boston Harbour as a protest against taxes that many felt were unfairly imposed on the colonies... A precursor in the escalation to the REVOLUTIONARY War).
Folks in the American Colonies drank coffee in defiance of consuming British tea (or maybe due to lack of tea supply).
Hence, the American "opened an old wound"
with an Englishman by saying that Americans don't need
kettles because we make tea by "throwing it into the harbor"
(Though, I'm pretty sure that neither Brits nor Americans are "opening old wounds" by Revolutionary War jokes and I'm not really sure why they used the pic from that Dodge commercial, except that it's cool as Hell and definitely AMERICAN!)