One of the oddest Britishisms I’ve heard is “moggie”, which means cat.
I was raised pretty much by my Scottish granny, now I am a terrible speller, eg. is it grey or gray. ive also used colloquilisms such as “no worries” and “grab a pint” before they were cool. It does worry my mates when i am a bit in the cups, when I say something like “och, Ah dinnae ken!”