I'm British, and some Americanisms really grate at times. Particularly when Americans insist that the original pronunciation stuck in 1672 when their 8 times great grandfather left the County of Rutland.
"go extinct" instead of "become extinct".
Using the comparators "than" or "as" instead of "to".
"Champing at the bit" instead of "chomping at the bit". How can a horse's teeth "champ" instead of "chomp"?
Pronouncing "herbs" as "urbs". I always have a vision of Grecian vases containing a quantity of basil...
"gotten" but not as a past participle or plural. Ideally, it should have a suffix and join "began" and "become".
These are but minor irritations when compared to how some non-native English speakers mangle the English language, in a misguided attempt to sound cool. Actually writing "wanna", "gonna" or "coulda". But worst of all is the use of "dear" for anyone younger than 80 years old.
The "it fit me" thing is weird too. It fitted you. Its a past or a past perfect tense, not a present tense.
"the English" when they mean "the British".
By the way, "could of" and "I sat" are northern English dialect remnants of a different language, probably Old Norse, in which they would have been grammatically correct. In other words, they are following the grammar rules for those accents. I quite like the preservation of old dialects and they often help with learning foreign languages.
British English is far more formal than a lot of non-native speakers like to think. And no, we don't all come from inner city London.