What British people mean when they say 'sorry'

I used to always put my bag next to me cause I don't want to sit next to someone (when I was a kid, it'd hurt me when I was solo sitting alone in whole bus, but I learned to embrace that instead). Nowadays, people just point at the bag, and during primetime it is just annoying having to ask (esp someone pretending to sleep, on phone, or lookibg outside) because yes we all don't like the bus is full, we all wanna get to work/home. So I learned to just start with my bag between my legs or on my lap instead. And, since the bag doesn't pay for a ticket, it has no right to a seat.

So in Borderlands 4, one of the voice lines by the Siren called Vex after a kill is 'sorry not sorry'. But given the CEO of that company is Texan, I couldn't pinpoint how rude (if any) that was. Not like they can hear you after a frag anyway.

Some British slang is just lovely. Such as smoking a fag. In that regard, too bad I don't smoke anymore.

But in the instance of sorry, I assumed it was American, since Brits would say 'excuse me'. Brits are, after all, very polite (I'm Dutch...)