If there's been any testiness or forgetfulness, it's minor. In the last 100 yrs, I see nothing but friendliness and alliance.
However, these reasons COULD be an explanation:
Firstly, many of us have no British roots whatsoever. In fact, within my circle friends and relatives, not a single one could trace their roots to UK.
Secondly, because Americans are aware of history as the 13 original Colonies had to overthrow the heavy-handed British colonial power with 2 wars.
Our respective governments have shown strong loyalty and strong alliance for the last 100 yrs. Throughout the period of time this very close alliance in WW I, WW II and many/most of the international conflicts. This bonding has been tested repeatedly and shown to be one of the strongest bonds in history.
Wasn't the whole US involvement in WWII proof positive of the undying support between US and UK?
Then withing TV programming there's the love affair with British humor and British programs. For example nightly BBC on cable, Monty Python, Fawlty Towers , Mr. Bean, Benny Hill (yuck) and a sea of other shows (Upstairs Downstairs), etc.
Forgotten? Where is it forgotten?