Americans call British People "Brits" or sometimes even "Limeys".
Sometimes Americans simply call British people, "British".
Although many American people also mistakenly call British people "English".
Calling British people "English" can be inaccurate as Britain also includes, Scotland, Wales and even Northern Ireland.
Brit is informal and generally accepted when referring to British people.
Although the context also matters, as it can sometimes carry negative connotations, which is similar to that of how some British people hate being called "Brits" as a result of associations with disorderly tourists.
Limey's is an older slang term for British people, which originated from British sailors' lime rations, and is used by Americans, although the usage of the term Limey's has also evolved.
The standard and respectful term and adjective and noun for citizens of the UK is British.
And Brits is the popular and informal shorthand for British people which is also similar to that of Aussie for Australian people.
Americans also often confuse British people, which are people from the UK, with English people that are from England.
This is a factual inaccuracy which can sometimes offend people from Northern Ireland, Wales and Scotland.
The term Brits can be okay when used in casual settings, although it may feel dismissive in more formal or sensitive situations.
And many people that are from non English parts of the UK, also prefer to be called Scottish, Welsh or Irish, instead of being called British.