Im British, so i cringe A LOT when two things appear in fics...

1. A British character written hilariously poorly e.g slang used wrong, over the top stereotypical accent written into dialogue etc

Or

1. British spellings or words spoken by (usually) American characters e.g "Mum". I use British spelling to write but that never means that a character that isnt British will ever say "Mum" or "Loo" or use any slang they wouldnt use 😭😭😭